From the recovery console (that you run from your XP CD) use the fixmbr command. That should be all.
http://www.google.com/search?q=xp+recovery+console+fixmbr will tell you all you need to know.
Please help me repair my MBR, I am not tech savvy. Looking for an easy program that will run in XP to repair my MBR. Please something simple. Thank you