I'm still running Win98SE on one of my computers. it's the most stable operating system I've ever had. I've had to reformat/fix something once. I've had a whole slew of problems with XP since I got it about three years ago. The ONLY thing I like about XP is it's ability to know what's plugged into it and find driver's automatically instead of having to install drivers... but then I have a printer, scanner, and jump drive, so that's all I've needed for it...everything else (PS2 controller, digicam, etc) goes on the XP machine.
I wont touch Vista with a ten foot pole. Neither will a good chuck of the country that's computer savvy. I think it's either Gateway or Dell who are still giving you a choice of which you actually want on a new computer. I'm thankful I got mine before the switch over. I think they were still calling it Longhorn at the time, though.