XP isn't "bad". It's simple to use and so long as you're sensible with cleaning it, won't often go wrong unless you do something incredibily stupid.
Vista is for style over substance, XP is for the power user. Besides, with various skins (or Windows Blinds, ty Niall
) you can get your XP looking exactly like Vista, apart from the "lets get all the taskbar icons into pictures on the screen and you can scroll round them in a floaty style.. thing"