I use Windows XP Pro, but I have still the windows 95 and windows 98se cds, just in case.... I've still got windows 3.11 disks somewhere. All 11 or so of them.
I used to have linux, which was nice, but it wasn't compatable with my onboard lan card. I had another lan card, but for about a year and a half I just couldn't be bothered to stick it in. I got rid of it when I finally plugged in my DVD drive which was sitting idle in its bay in. I have a crazy RAID motherboard, which I don't use or need, but I have to switch it on if I want to use more than two IDE slots (which I do). But then linux won't boot (it can't recognise it, and I can't be bothered to fix it). So that's my story of why I got rid of linux. The fun of trying to fix the problems far outweighed the actual benefit of keeping linux on my system.