You might need to tell a little bit more.
- your exact disk configuration (how many IDE and SATA disks)
- the exact error message (for the message you quote you're the only hit in google; that's amazing isn't it, your post already is in google with the time stamp "2 minutes ago")
- how you access the Windows XP setup
- why you access the Windows XP setup
- what version of Windows XP (original, SP1, SP2, SP3)
Also please download a Linux Live CD (Ubuntu or so) and boot from that. What does it say about your hard disk?
I checked BIOS on Harddrive it says its connected [SATA(bunchofnumbers)].. But when I ever try to get to the Windows XP setup it doesn't go, it's just a black screen saying 'Error operator system'
and when I unplug the (red/black/yellow) wires I can access the Windows XP Setup... It's weird.. but it seems like everything is plugged in perfectly.