afaik RAID only works on SATA drives
RAID was invented long before SATA.
Jon, That RAID card should have came with a CD. Have you ran it?
Are you saying that you had three hard drives on your RAID card and added the 120 gig seagate after you had your array set up? Or did you just hook up four drives and the 120 gig seagate was the only one not recognized by your operating system?
Are you trying to Run RAID1? I would suggest using a RAID 5 array.