This is what I was told,
"Assuming that you have RAID1 [Mirror] Boot the system, enter the RAID BIOS setup, select Delete Raid Volume and set the drives to a non-RAID configuration.
With RAID 1, you should have 2 hard drives that are exactly the same, after this, you can partition and format the second hard drive.
You will receive a message saying, the RAID volume data will be lost, this is a true statement for RAID 0, but not for RAID 1 and can be ignore, your data on the RAID 1 volumes should be safe.
After exiting, you should see two hard drives as Non-Raid either immediately or after a reboot."
So yeah... Anyways, I pulled out one of the drives to see if I could reformat just one of them, but then the RAID went all crazy and Windows wouldn't even recognize there was a drive there. I put both back in and just completely removed all RAID settings, reformatted both drives together and then finally was able to reinstall Windows on just one and the other is now formatted and blank... and RAID free...
Luckily my computer does a weekly backup to an external hard drive, so I didn't end up losing much. But it was quite the experience...