Good stuff accumulating in the thread.
For future reference, just in case you get stuck:
http://support.microsoft.com/mats/cd...problems/en-us
Tell us the HP PC model/part number along with the BIOS manufactor and level. That will help bridge some of the gaps and narrow down any possible solutions, or, eliminate any possible mistakes.
Not to dissaude you but understand the upgrade to a SATA device is going to problematic since XP was pre-SATA.