just got cod4. bought new nvidia gforce 8400 gs (pci) card to run it. game loads with small glitches or lags and then freezes after a few seconds to a minute of play. have tried changing settings and closing all background apps but nothing helps. i have a pentium 4 2.8 GHz cpu, 1 gig ddr ram, sound blaster audigy sound card and plenty of disk space. can anyone help?