Windows 7.
But in this case, I was actually talking about the Itunes app. It was working fine, and then one day refused to let me access the exe (Something about administrator privileges, which was never a problem before, but which I tried changing anyways). In the end, I decided to try an uninstall/reinstall, and now it doesn't seem to even recognize I'm using "At least Windows 7 service pack 1" (I'm using a higher service pack, only not up to date.)
Only thing I changed on my system was installing Firefox and Mcafee (Which is bundled up with the package), decided I didn't like either program, and individually uninstalled both. Also, I've tried syncing Windows Media Center with a 360 for streaming media.
Maybe that did something? It's either that, or an Itunes update which requires a Windows 7 update I've been putting off. (I know, you can say "just do it", but this "play system" has very little horsepower as it is. The thing can't even run Aero without lagging videos, and as you probably know Areo enables a lot of Vsync support. Some apps like Windows Media Player don't need it, but Youtube videos, streaming, and games get tearing with Aero off. As lagging is the worse sin, I leave Aero off..)
Bottom line, I only wanted Itunes for downloading some podcasts, and occasionally transferring things to my Ipad.
I'm probably better off just using Podbean and Dropbox at this point..