I was using the X64 edition for a while, and the game itself runs, but none of the addons I tried worked. Couldn't get the high res patch or the sound patch to work. The only thing I noticed was that the game itself was stored in a slightly different regestry entry. Everything else was the same as it is in any prior OS. Just one of the reasons I switched back to the regular Pro VLE edition. I even created a thread somewhere asking if it was possible to fix it, but nobody ever responded. Not even a "sorry can't help" reply... just... nothing.
EDIT: Yes, I tried it on Vista as well a few months back, and it seemed to work fine. Didn't try any of the addons with that at the time though. Quickly stopped using it due to so many bugs that were in the system. For the heck of it, after I found a bunch, I gave my friend (who's as good with computers as me) 20 minutes just looking around on the OS. Testing stuff and such. We found so many bugs that we agree: we don't see how it's going to make the release date they promise. It's way too buggy.