Lol @ nobgoblin ... thanks for getting all the stupid arguments out of the way already.
I'm with Naheal, laptops have trouble playing games unless the games are old (I suppose WoW counts, but I wouldn't want to try it on mine after seeing the framerate on my bro's previous
desktop) or the laptop is expensive. The mobile graphics chipset is the problem. Though if you get something like the radeon in ^that Acer^ (from that or a different brand) you'll be alright - actual gaming gfx hardware, there.
Cheapest gaming laptop, though? That'll be the one I picked up for £40 (say, $60) a few years back that would play GTA (...one) and all of iD and Apogee's finest VGA ModeX hits quite happily. Once you've exhausted what GTA 1, Descent, Doom, ROTT, Quake and all their respective expansions have to offer, send it for recycling, you've had your money's worth

(Can probably update that to the initial GTA3, Driver, AvP and their contemporaries now)
Heck, how much would you give us for a 5 year old, 12" ultraportable that'll make a decent fist of Live For Speed?