Even more nice Mac verbiage from the Install Photosynth page:

Operating System: Only Windows XP (SP2 or SP3) and Windows Vista are supported at this time. Running Windows on a Mac? Photosynth runs under some VM configurations. Check out our help site for an updated list.

What's the world coming to? I mean, I think we all know that Microsoft hates what they want to term Naked PCs, and, well, most Macs running Windows are -- again, just conjecture here on my part -- running illegal copies, at best from people "concurrently licensing" the copies they bought for other hardware. But here, a MS site is all but begging you to using Vista on a Mac using a VM.

Hrm. Photosynth must be phoning home too.