When I made a thread for building a computer I was told that the only real difference between the two was that the i7s had hyperthreading and that this wouldn’t make much of a difference if using it for gaming. Although I’ve noticed that i7s tend to have higher clock speeds but if you really felt like it you could overclock an i5 to pretty much the same speed.
One thing I forgot about are your drives as well.
You’ll need a SATA II CD-ROM (DVD-ROM, DVD-RAM, whatever, they’re all the same now) drive. I bought the cheapest one possible, an LG for 25 bucks, and it’s good enough. I just use it to install my operating system.
You’ll also need to buy a SATA II Hard-disk drive. I’d recommend a Western Digital Caviar blue, either 500Gb or 1Tb. I have the 500gig, and I think it was about 50 bucks.
And yeah, the i7’s are just bigger and more powerful. Some have hyper-threading and some don’t. The models step up, like one will be around 3Ghz and have no HT, then the model up will be 3Ghz with HT. You can read about the particular CPU’s features and decide based on your budget. I don’t think any of the i5’s had HT, but some were only dual-core. Hyper threading is like splitting each of your cores into 2 tasks, so it’s kind of like you have 8 CPU cores, but they share the resources of 4 cores. Gaming performance increase is negligible.
I’m running a server from the computer so I need some kick behind the CPU…so the i7 it is
I would recommend going with the new generation of i5’s and i7’s with P67 socket.
Motherboard
ASUS P8P67 Deluxe $225
Processor
i7 2600k $315
DD3 RAM
Gskill Ripjaws 4 GB 1600 mhz $55
HDD
A good 7200rpm sata3 drive (maybe get two of these: Caviar Black 500gb)
GPU
Sapphire Radeon HD 6970 2GB $350
Power Supply
Corsair 850W $134
Case
Whatever you want - about 150 bucks.
That makes for a grand totale of $1350.
You can spend the rest of the money on
-an optical drive (a DVD reader/writer goes for 25-35 bucks)and/or
-more serious cooling (such as this cooler: Cooler Master hyper 212+ $50) or
-an SSD (expensive!!!) or
-more RAM.
As for assembling it, it’s not too bad in terms of difficulty, but there are a few things you should know:
-Take anti-static precautions. I just touched the inside metal frame of my case occasionally as I assembled it to discharge static, but you could go so far as to get a static-leash or something.
-When installing the CPU, follow the instructions that come with the mobo and the CPU. When you put the cooler on, the thermal paste will be pre-applied so DON’T TOUCH THE BOTTOM OF THE COOLER. Just push it straight onto the CPU, one snap at a time until they snap. I had to push pretty hard to get them to snap. It’s a bit of an unsettling experience the first time, but it’s normal I guess. Putting in the CPU is the hardest and most important part. After that, it’s a cakewalk.
-Make sure your motherboard standoff posts are in the right place for your motherboard before you put it in. Those are the little brass studs that you screw the motherboard to. One stray post and you could short circuit the whole board, and the warranty will not cover improper installation.
Other than that, just read some tutorials online, it’s pretty easy. This goes there, this plugs into this, etc. I’m sure the guys on here would be happy to help if you run into trouble.
@acade - Yeah, that looks more modern, I’d go with the 2nd gen Intel CPU’s too now. I’m not up on the hardware anymore since I haven’t been shopping. I’d imagine the HD6xxx cards are the norm now, are they?
EDIT: One other thing you could consider is where you get your stuff. If you’re impatient like me, you could go to your local computer parts store and just buy whatever they have there (If they’re decent at all, they’ll have the latest hardware) and they will make sure you pick the right stuff and that it all works together for you. They may even build it for a small fee.
Or you could spec an exact machine and order the parts online, which you might be able to save money at.
I would push purchasing the parts online. Newegg is doing this thing with a company called shoprunner right now where you can sign up and get free 2 day shipping on everything. You just have to cancel it before the trial period is up or pay $70 to keep it for a year. It saved me a small fortune on some recent orders. Shipping costs on big stuff like cases can be painful 
In terms of parts, build around the processor. As far as I’ve seen, Intel is only worth it if you’ve got the money. AMD processors work fine if you want to put the money into something else. It’s also been mentioned before, but it can’t be stressed enough to get a case that is big enough to hold huge graphics cards and still have good airflow. I have an Antec 1200. It’s huge, well made, and I could almost live inside it. I would also recommend buying the power supply as one of the last components. You need to tally up an estimate of how much power your system will use under full load. 750 watts should handle a system with a single high end graphics card, but if you want to do sli or crossfire you’ll need around 1000 watts.
Basically all you have to do is decide what you want it to be able to do and then check the parts for compatibility. If you go with newegg, make sure you read the reviews and look for combo deals. Subscribe to their newsletter to get the promo codes too. I’m sure most of the people here would be more than willing to help you make the right choices. You’ll save a ton of money and come out with a rig that can run circles around anything you could buy pre-built for the same price. Not to mention the fact that you’ll come out with some cool learning experience.
He has a 1500/2000 dollar budget, so I don’t really think money is a problem.
Don’t forget custom CPU cooling, and I recommend going for 6GB triple channel memory.
And don’t forget to set the memory timings and voltages when booting the PC, I can’t stress this enough. There’s always some new guy who doesn’t do it and finds out his PC is locking up randomly all the time, or that it’s unstable, performing badly and so on. Timings and voltages are located on the sticker on the memory.
^ If you are going for my recommendation (P67 rig) get double channel memory instead (2/4 sticks instead of 3/6)
I’m getting this mixed vibe about custom cooling. I don’t plan to OC so I don’t think I need it.
Never go for stock cooling, regardless of whether you’re overclocking or not (you should always overclock anyway). Stock CPU cooling always has ridiculously high temperatures on both idle and load. An overclocked CPU with custom cooling is likely to have a lower temperature than a factory clocked CPU with the stock cooling.
For the most part, I’d say you NEED custom cooling. Get a case with good airflow (check reviews), and one of these for the processor: https://www.newegg.com/Product/Product.aspx?Item=N82E16835103065&cm_re=hyper_212%2b--35-103-065--Product. It’s only 50 bucks on newegg and it’s even cheaper on amazon, and it’ll make a huge improvement.
To all the custom cooling enthusiasts - how many cpus have you actually burned out?
It’s not just about keeping them from burning out, it’s also about prolonging the life of your processor and keeping the entire computer’s temperatures/noise levels down. A $30 custom air cooling solution will be worth it in the long run, whether you’re overclocking or not, no doubt about it.
I got my AMD Phenom II X4 970 at 3.7, idle temps 36-38c. in games 40c-45c.
Of course, I’m not saying stock coolers are good, but not every stock cooler is totally useless. (still recommending a custom cpu cooler)
It’s pretty hard to burn a CPU, you’d have to exceed the thermal threshold quite a lot (for Intel CPU’s that’s about 91 C if I remember correctly). Custom cooling is not primarily about preventing your CPU from getting fried, but to prolong its lifespan. Low temperatures also allow for a much higher overclock. Intel i7’s are known to be excellent overclockers, you can get a lot of extra performance out of the CPU without extra spending money. Custom cooling usually also means better airflow inside the case and a lower overall temperature for the motherboard (motherboards really hate heat).
Depends on room temperature, dust in the heat sink, age of the CPU etc. Try stressing your CPU with Prime95 and check the temperatures after 10 minutes of number crunching (it’s usually used to check for overclocking stability).
…which was my point. So how many cpus have you burned out? There is no point in having your cpu run at 30C so that it outlives your grandchildren. You’ll scrap it in a couple of years anyway.
Congrats to you if you have the money to “scrap it in a couple of years anyway”, but the computers I build I expect will last me 8 years without major problems. Why would you risk damaging your processor after only a few years of use when you could spend $30 and make your entire computer quieter, cooler, and live longer?
Whoa, sudpuzzer… why do you have to get a brand name psu? Not that I doubt your expertise, I dont know too much about building computers at all. I always thought that the brand didnt matter as long as it had the right wattage. (i think i know the least abotu psus out of computer parts. :p) i got some cheap offbrand psu for both of my computers, a 500 watt for like 20 dollars each and they both are still running three years later for one, 1 year later for the other. 
LOL, I was exaggerating a bit there. 
I’m currently running a P4 from '06 OC’d as high as it goes and it’s still very much alive. Can’t run games on hot summer days though. 
[EDIT] As for the PSU, I’ll have to say at least a decent one is a must. PSUs are the only components that have ever died on me (and not just one but three).