Yes, Windows 7x64, but has also been used on XP … MOTU appear to have the same driver “package” for all. I just have a little bit of a thing about MOTU … their Windows support was flaky up to a few years ago, favouring Mac, but most of all they simply refuse to consider supporting Linux (but then again, neither do Steinberg!). The MOTU Express XT is even more useful if you want to edit hardware synths because of the patchbay functionality, and I think in the meantime may be unique on the market for that reason. Maybe I’ll grab one before MIDI is “obsoleted” entirely …
(By the way, there are many MOTU Express XT’s being offered second-hand, but almost all of them are the older parallel-port version, so if you’re in the market be sure you’re getting the USB version!)