I had vista, but it broke and would freeze up for 2 minutes while it was trying to detect my internet adapter. So I just went back to XP. Maybe when SP1 comes out it will be way better.
It's amazing how fast xp default is.. but its incredibly shitty when it comes to most other things... SP2 makes it slower to boot, but it just makes up with it in security. I think sp1 is kinda a good balance between the two... and sp3 is supposed to be coming early next year. But I wouldn't run XP without sp2 now, it's just too damn easy to infect with shit.