If you are trying to load XP onto a RAID volume onto new HDDs, you will have have to create the volume through the BIOS.
-- First you have to set the BIOS settings for the HDDs to RAID.
-- Save and Exit BIOS. Then, during the POST screens, you'll get a screen to create RAID array and volumes.
-- Press "Ctrl+I" to creates the volume: RAID 0 or RAID 1, etc., select the HDDs and volume size.
-- Save and Exit the BIOS.
-- Load your XP installation media.
-- Boot to the XP installation media.
-- Press F6 to load your RAID driver (unless you added the driver to thea custom install using nLite).
-- Load the RAID driver when XP asks for it.
-- Continue your XP install.