MAYBE this is what happened. Windows Vista (and its Install routine) can use IDE or SATA HDD units, but it cannot use a RAID array unless you use a special routine early in the Install process to add a device driver (must be read from a floppy disk or USB drive). So if your BIOS was set to configure the SATA unit as a RAID device, Windows Install could not use it. If you changed that BIOS SATA Port Mode to IDE, or to native SATA, or to AHCI (the real nature of SATA drives) , the Install routine CAN use those device types because it has its own drivers.