You don't mention how much memory your video card has compared to how much memory is on your friend's NVidia card. Lag, most times, is due to memory differences. You listed your system memory for both machines at 2 gigs but the video card ememory is also a contributing factor and video cards come with varying amounts of ram onboard as well. There's also the speed factor of the ram to consider. Different memory sticks are rated at different speeds.

It is a miracle that curiosity survives formal education. - Albert Einstein