Yes 64bit windows 7 works without a problem. The motherboard itself only officially supports 2 gigs of ram though. Apparently there's some workarounds for it, but I never used them.
If your using an exotic GFX card like I was, 2600XT AGP, I'd strongly recommend downloading the appropriate drivers (or vista hotfix drivers in my case), prior to the installation.
The system itself doesn't feel sluggish at all on my dualcore email@example.com and boots a lot faster than XP ever did. By the way 2.5ghz was the highest stable overclock I could get on this ASrock board. Never bothered doing a BSEL mod since I just bought a new system altogether.