XP +1 As much as I dislike Microsoft in general I'll have to admit - XP runs stable as hell, I never had any problems with driver support (at least not in the last 5 or so years), which I can't say for Vista (possibly add a "yet" here). It runs on fairly low spec computers without any problems, too. I've ran XP on an old Pentium 200Mhz with 64MB RAM - it's a bit slow, but not horribly. Vista does come with some interesting improvements, but it's just not "there" yet.