You’ll have trouble running TF2 on medium on that HP. I have a Dell laptop with an 8400gs (more powerful than the ION in the HP) and it struggled with tf2 on medium settings at 1366x768 (common netbook res) during heavy fights.
I’d suggest a small 14.1" laptop with some sort of dedicated graphics, like nvidia’s optimus switchable graphics. That’ll give you good battery life, portability, and some gaming ability.