I'm not running crysis or something, just like HL2 or Garrys mod.
Ah, in that case an $700-$800 laptop should get you somewhere around 100-200 gigs of HD space, a dual core 1.7 or better and at least a gig or ram.
for Garry's mod you'll need more than that, 2.2 dual core should do it and a good amount of video memory (this should still be less than $1000).
As for what video card, you'll be stuck with whatever is in what you buy because they can't be changed, the problem there is that good video cards only come in good (expensive) laptops.
Because of the video card problem in laptops you are much better off getting a desktop.