Ah-hah! 1) What version of XP? 2) What mode (AHCI, RAID, IDE) are your motherboard controllers set to in BIOS?
My guess is that your XP installation disc does not have the drivers needed for your motherboard / drives, probably because the controller is set to AHCI mode and it's an original XP disc.
In that case, you would need an XP Service Pack 2 installation disc or to add the proper drivers during the Windows installation process. You can build your own SP2 disc by looking up "slipstreaming."
Please let me know if this is, indeed, your issue.