I have a sabertooth X58 mobo and have set it up with two seagate 250GB HDD's and installed windows 7 fine. It works great, but i have added a 2 TB Hitachi drive for extra storge. The drive is seen in the bios and appears on the screen after POST displaying the RAID configuration but when i load windows the drive is not there.
go into drive manager, locate and initialize the drive.
start> rt click Computer > select Manage > on left pane select Disk Management >
in lower center section locate the drive which probably says Not Initialized and rt click it and select initialize. >
now that its initialized it should show as Unallocated . rt click again once and select New Simple Volume to begin the wizard.