XP SP2 is no guarantee that you won't need to install seperate RAID drivers. It all depends on the RAID chipset. If the XP installer doesn't see your RAID drive then you need to install the drivers.
There should be a copy of them on the CD that came with your mobo but they need to be placed on a floppy (they have to be on a floppy and you must have a floppy drive installed - even if it's a USB one). Comtimes there's a folder with the 3 or 4 files you need for the RAID that you just copy to a floppy, and sometimes there's an installer that creates the floppy for you.
Press F6 when prompted by the XP installer, then wait and insert the floppy when prompted.