that's because you need the SATA drivers -- these aren't normally included with Windows XP.
If you have an option in the BIOS you *might* be able to change the disks to IDE emulation or something like that then it should work.
Otherwise you need to "Slipstream" SATA drivers into the XP install disk.
There is an excellent way of doing this if you install and follow the instructions and links from here News | DriverPacks.net
Look for the documentation and follow the instructions
I used these for "De-Vista-ing" some laptops a while back (pre Win 7) when VISTA was running like a dog and I wanted to un-install the pre-installed Vista and install XP on them.