I still use XP - having a look to see if I should go to XP x64. Still too lazy to try Linux, though I have a little bit of experience in it.
Windows XP SP2 Professional.
I also got Vista Ultimate >< but my DSL modem and Printer isn't capable with it lolz.. so i have to keep with XP
XP.
Has most support = 1/2 the programs don't run on anything else.
Windows XP Pro SP2
I'll probably get Vista Ultimate later this year when I get a new computer, but it depends how much they have improved it by then.