What version of XP do you have installed? OEM, Retail, VLK?

Search for converting the version you have to VLK.
needs registration to read http://www.experts-exchange.com/Operating_Systems/WinXP/Q_21192535.html

Maybe Win Keyfinder can help http://www.aplusfreeware.com/categories/util/registry.html

Do you have an image of this drive already? If yes, a reinstall of XP using the repair option with the VLK CD should leave only windows updates and maybe drivers to reinstall.

If used this option for two motherboard upgrades now as I really didn't want to reinstall all my software.