In the BIOS check to see that IDE HDD detection is set to Auto, and Access mode is Auto. Make sure HDD boot priority is set for your SATA drive. And for BOOT order, make sure HDD is one of the choices you have selected.
If that is Ok, did you install the SATA driver when XP setup asks you to press "F6"? The driver is probably on the CD that came with your MOBO. XP will want you to install the driver from a floppy though.