If you did a Repair Install from a standard issue XP SP1, you may have a case of the file version incompatability that can happen with Pavilions, between the original HP install & the MS one.
This may help:
http://support.microsoft.com/default...;en-us;Q329450
Your situation may be the last symptom nominated:
"If you try to reinstall Windows XP SP1, the installation is unsuccessful."
(Edit: Although, this looks as though it only applies to recovery to original HP spec, which is not what you want... HP ... :rolleyes: )