Hmmm...have you attempted a repair install of XP?
A repair install will leave programs and data files intact...and will remove all XP system files and replace with clean ones. All critical updates installed since issuance of the CD used...will be wiped out and have to be reinstalled via WinUpdate.
The smart thing to do (if your CD does not have SP2 included) is to slipstream a new XP CD which includes SP2 (and SP3 if you have that currently installed)...before attempting the repair.
Perform a Repair Installation - http://www.microsoft.com/windowsxp/using/h...ips/doug92.mspx
nLite - Deployment Tool for the bootable Unattended Windows installation - Guide - http://www.nliteos.com/guide/