Just found this website and seems very good one at first glance. But there is something I'd like to ask for a start. I'm little worried how my computer is going to perform with the Modern Warfare 2. I was able to run COD4 and COD:WaW with highest settings and 1920x1200 resolution, but I think that with the MW2 my loyal and gutsy computer has found it's match.
Windows Vista 64-bit
(note: your graphics card is a little bit better than the referenced 9600 GT)
I do not know how CPU bound CODMW2 is, but keep in mind that the above referenced link tested the game with a high-end Core i7. Nevertheless, I still think you will be able to average 30 - 40 frames. It is not like you are using a 8800 GT and a Pentium D. You have a decent quad core with an OK frequency. Also, if you get game and discover that things are not working out, consider overclocking your CPU or doing a simple upgrade (ex - 8800 GT to HD 5770).
Modern warfare 2 is built on the same engine as the original modern warfare. This is good, and bad. It has been upgraded/tweaked as much as possible without implementing a newer engine. This is good for users with older PC's or only mid-grade graphics power. It is "bad" (not really bad, just could be better) for enthusiasts with very high end machines, because it will not truly utilize the extra power their PC's hold. Activision was smart in making the game this way, because they will be able to market the game to many more people...it will not be as high-end-exclusive as say, Crysis.
This means that it will play on many more systems than if they had used a new grapchis engine. Older machines should be able to run CoD MW2 on medium settings. I suspect your machine will run the game just fine on medium to high (likely no AA though).