I'm having the same issue Simon, it's not your hardware. Well, it is your hardware, but specifically, it's the fact that Windows 7 can't support your hardware yet. It seems to be an issue with owners of certain Asus mobos with Athlon processors.
I am running:
Asus M2V-MX mobo
Athlon X2 6000+
2x2048MB Kingston RAM
Before Windows 7 I was running XP Pro-64 with no problems. Then when I tried to run a clean install of Windows 7 everything froze until I took out 2GB of ram.
It's been mentioned in several forums. This thread seems to have a BIOS tweak that may help some people, but it's not an option on mine. Anyone have issue with installing windows 7 x64 with 4GB ram
Unfortunately, that stick of RAM might have to sit in your drawer until Microsoft comes up with a patch.