I have V5 R18 64-bit running on my Win7 RC machine, just for fun. The install was a bit obnoxious, UAC and all that. I am using the x64 version, and a gaming video card. It all seems to work fine. Of course, this is on my home pc, not my workstation. LUM installed only in administrator mode (windows) and then I VPN in to the work network for a license.
I would add in all the usual bits about certification of hardware and drivers and combinations thereof. But, I'm assuming you're asking a curiosity / hobby oriented question anyway...
Cheers,
Mark