It sounds as if you have the original XP CD, which has been updated with XP2 & other updates.
I would suggest you use the repair option on XP , however this is not straightforward using an old (original) CD.
Go to the microsoft site and download the XP boot file for your version of XP.You will need 6 floppy disks.Follow instructions to create floppy boot disks.
Set your machine to boot from floppy, insert floppy 1 into the drive and your XP CD in the CD drive. Re-start machine and follow instructions.
Ignore the first repair option.All going well you will come to a blue 'Terms and Conditions' screen -Press F8 to continue, the press ESC for advanced options. Select the R for repair, and allow XP to check your system-remove and re-install files as required (Automatic). You will need the XP Code, and you will have to re-load your XP SP2 and all updates, however all other programs on your system should (no guarantee) be ok, with the exception of any EMails, addresses etc which will be lost. This will repair your system.