If you dont want to spend very much money, I would DEFINETLY not go with a laptop. If you want something for mobile gaming, expect to spend some extra money. ALSO: alienware is overpriced.
I wouldnt skimp on a laptop if you really want one for gaming.
Dell XPS m1710
you can build a PC just as good, if not better for half the price.... But mobility is really the only thing costing you here.
NOTE: My laptop has 1 Gig of ram, 256mb video, and a 2.0Ghz processor, but I payed $1100 for it. Laptops also get hot too quickly, making them inadequate choices for gaming.