A while back I bought a PC from Ebay which is working fine. It has XP Pro on it but came with no disk or sticker. I have tried and failed to upgrade to SP2 and I'm now told that I have a bad corporate key' and that my copy of XP is probably illegal. Which is nice. So, I need to rememdy the situation. I don't really want to bother with a re-format as I have loads of stuff on the PC but I could at a last resort. I have seen people selling legitamate boxed versions of XP Home for not much and figure that is the way to go to become legal again (I assume it's legal to buy a second hand OS)! If I buy a CD and key sticker, what is the best way of installing it. Can I just do a repair install and enter the new key, bearing in mind that I'm putting Home over Pro? Or do I really need to think about a full format?