I just brought a brand new desktop. Gateway GT5692 4G DDR2, X64 Home Premium, ATI Radeon HD3200, with AMD Phenom 8450. I install the COD4 and the game play is so choppy! My friend has this game running on an older XP pc and his is running great....What could be the problem? Anyone please help....cause I feel like an idiot buying this desktop for almost 600 and can't play Call of Duty 4.