Gaming on a laptop can be an interesting experiance. I was using a friends HP or Compaq, can't remember which, to play a LAN Halo game on, graphics were ok, but it got REALLY hot, so much that unless I put it on risers of some sort(used pencils) that it would overheat and crash. Add the fact that the price for a laptop decent enought to game with for several years is far to high in comparison to a mobil only laptop, throw in the upgrade issues with laptops, and I didn't get a gaming laptop for college. Enough ram and a decent GPU will run a lot more than a desktop.
So, here is another vote for the G4 12": light, mobile, good deals can be found.
IF you are wanting to get a better gaming setup, a new video card is all that you would really require. Dual channel ram and a nicely OCed processor are not holding you back.
My two bits.