I run XP on my mini with 512MB of ram and am pretty happy with it, but I don't do a lot in windows. I play some videos with VLC and use IE6 (via Virtual PC), IE7 and Firefox for testing via VNC. Sadly windows is much better for my uses on this machine as a media machine (due mostly to the advanced features only available with the windows video drivers to set different color curves for the video overlay -- something OSX doesn't have).