If you're looking for a laptop that can run GTA IV on at least minimum settings, I've tested an Acer Aspire 4740G with 2.3GHz Core i3, GeForce 310M, 2GB RAM (can probably be upgraded; Acer also offers i5 and i7 variants of the 4740), and I often get 25~45fps on medium, with the resolution set to 640x480, although there are some occasional lag spikes.