No no sorry, I didn't put it clearly.
Win7 is very flexible when it comes to component changes.
I had a Win7 machine running for 6 months on a old M/B, Dual core and SLI 8600GTS, then I took the hard drive out and changed all components in the computer apart from my powersupply. I put the hard drive back in and booted. It took a few restarts (and driver installs), but the computer was then running on a totally new system but the same hard drive.
I'm still running that OS today, a year and a half on.