I just installed Call of Duty 5 - World at War and it runs very slow. Is there anyway to get it to run better?

My computer is about 6 years old, but I am running Windows Vista Business SP1 on a Pentium 4 3.06GHz w/ HT, 2.50 GB RAM (DDR PC2700 333MHz), 512mb 7300GT AGP nVIDIA video card, My primary HD is an 80gb 7200 RPM (IDE ATA 133) Western Digital, but the game is installed on my secondary HD (650gb 7200 RPM SATA (which is running through an IDE/SATA to USB connector) Western Digital. I have all the games display settings set to the lowest you can get (640x480 and all graphic/texture settings low too) and the game runs as if I have a P3 500mhz w/ 512mb ram. I checked the games recommended settings and I have everything beat by a long shot, although my CPU is right at the recommended speed. I tried installing the latest video drivers (v182.50 from nVIDIA) but for some reason they didn't load, so I went to v178.xx instead and did not see any change. Is Vista Business OK to run with? I could drop back down to XP SP3, but I have too much stuff on my PC and I don't want to lose my data. Is there anything I can do to make the game run better than it is?? Any help would be great! Thank you in advance!!