I'm quite sure that a repair install can be done without having to reinstall applications!
As I said, I haven't done it myself with XP yet, although I have done this many times with previous versions. Have a look at this site for the details:
http://www.michaelstevenstech.com/XPrepairinstall.htm. It states that "A Repair Install will replace the system files with the files on the XP CD used for the Repair Install. It will leave your applications and settings intact, but Windows updates will need to be reapplied."
Obviously if you can get the swap done without this, then so much the better.