You could try
http://www.michaelstevenstech.com/XPrepairinstall.htm
especially
Possible Fix by reconfiguring boot.ini using Recovery Console.
1.Boot with XP CD or 6 floppy boot disk set.
2. Press R to load the Recovery Console.
3. Type bootcfg.
4. This should fix any boot.ini errors causing setup not to see the XP OS
install.
5. Try the repair install.
One more suggestion from MVP Alex Nichol
"Reboot, this time taking the immediate R option, and if the CD letter is say K: give these commands
copy K:\i386\ntldr C:\
copy K:\i386\ntdetect.com C:\
(two other files needed - just in case)
1. Type: attrib -h -r -s C:\boot.ini del C:\boot.ini
2. Type: BootCfg /Rebuild
which will get rid of any damaged boot.ini, search the disk for systems and make a new one. This might even result in a damaged windows reappearing; but gives another chance of getting at the repair"
Good Luck!