Perfermance issues with borderlands

I just bought borderlands lately but the game seems to lag at 1080p i used fraps and the fps never drop below 30 but it feels laggy. I tried to disable the mouse smoothing alraady but it didn't work.

Specs hd 4850 512mb

core 2 quad q8200

3gb ram

win xp

thankyou

I think it might be your video card. I know it's good at 1680x1050, but it might struggle a bit at that resolution. Something around the performance level of a 4870 might be better for 1920x1080.