Hi,
I strongly advise you to make a backup of your XP system partition before attempting anything with recovery console repair of the MBR. I had an unfortunate experience with that recently after Ghost 2003 had done something to the MBR and when I attempted recovery console repairs I got a warning message that the edit was not advised. I proceeded anyway. Result: system hosed, reinstall of OS necessary. Be careful.
You may want to look at the problem from the Linux side of things. Perhaps during the Linux installation GRUB or LILO makes a copy of the old MBR before changing it and stores it somewhere in the Linux distro. Worth a check, IMHO.
--torandson