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”