Don't panic yet. Disconnect both disk and reconnect the faulty disk to SATA0, then try to install XP to it (using the usual F6 command to install the SATA driver). If it boots up to the installation screen, then the disk is okay and it must have been a problem with the array. If so, it could simply be a faulty driver; RAID drivers are usually okay but I've experienced the occasional flaky one. Check for newer revisions just in case. What chipset is it?