Check this out m8;
http://dangerdogz.com/forums/topic/10946-will-i-have-to-reload-windows/
It was really simple. Windows7 sorted it all out and I merely had to re-register my copy with Microsoft. No problems.
I run with 12 gigs of ram though really 8 is enough. I've been really pleased with the results. The big difference was in how it made RoF run as - at the time - it was the only game I had that was designed for quad cores. It made a bigger difference than upgrading my gfx card. Everything was smoother, faster.
I ended up overclocking it even more up to the 3.8ghz it runs at now. I wasn't difficult, I made a YouTube search for my chip and found loads of useful stuff.
Dosen't CoD run o.k though? It was designed for single/dual core cpu.