Trying to assist another who has an XP home machine. Apparently, the recovery disc does not support repair... only reinstall. I would like to assist by using my XP Pro disc using the repair option. Would this work with the different OS versions? Guidance sought

Yes. You can use your XP pro disk to start the recovery console and make changes to XP home. I just fixed a Dell this way... It was stuck in a restart loop caused but a virus. The XP pro allowed me to find a backup boot.ini file so I could install and run Anti-Malware programs. After cleaning (three days later) I chose the original boot option and "bang!" I was back in business. I removed the second boot profile and ran more scans (Avast - boot-time) and it found more!

You cannot repair the install automatically, though (if I remember right). I think I tried that years ago with no success. If you try it and it does work, let us know! If not post your issues here and I try to help you through it.

Good Luck

There could be other options, but we need more information about the computer and the problem. Please post back with much more information. Computers like Dell, HP etc, have a copy of windows on a hidden partition on the drive and by pressing buttons on boot you can access this partition and repair the machine without wiping everything.
When you install or do a repair/install, Windows XP, the media must match the product key. That is, the channel (MSDN, retail, OEM, Volume License, and so on), the SKU (Windows XP Professional, Windows XP Home Edition, and so on), and the language (English, French, and so on) must match between the product key and the media. This is necessary so that you can successfully enter the product key. If the installation media does not match the product key, you receive the following error message:
"Product Key is invalid."
Have a look at this Youtube video to see about using UBCD to repair the machine.

commented: you shoud not be low +1

Was your problem resolved? If so, post the resolution and mark the thread solved please.