Sorry I missed your post - haven't been here for a while.
Yes, I've played many very good fan missions in the past few years, mostly selected by cruising the threads at TTLG. I'm due for a downloading session very soon, in fact; haven't downloaded any for about a year, so there should be some new great ones. Some of the series missions are fantastic - Elizabeth Bathory, and Dracula Reloaded, for a start. Some of the newer, larger fan missions are better than the originals.
I actually bought myself a laptop with XP on it, just so that I could play the the first 2 Thief Games (as well as my other old faves like Deus Ex, BG and PsTorment) without any hassle. On the Internet I also found a copy of bundled Thief games that will run on XP and Vista (including Thief Gold), but no idea if they would run on Win 7.