Question for anyone who knows. *NOTE NOT ASKING FOR KEYS!* * I bought XP Pro, have the CD and reg key number for it. I put that version on my computer. Have download SP1. I am building a computer for my sister for x-mas. I want to put XP on my sisters computer. Should I use my serial or another serial? How should I go about it so I don't loose my SP downloads and be able to download SP1 on hers? I know all the serials I got have probley been used, so whats my best bet?