Need more info? I can't believe this situation has never come up. Bueller?
Given that your OS is on a different controller what you want to do is certainly possible; changing the Intel controller to RAID should have no effect on the OS drive.
You would need to back up all the data from your data disc as the act of creating the RAID will likely destroy all existing data on the drive(s); although simply turning on the RAID in the BIOS will not affect your data, the controller built in to the motherboard is likely to be too basic to have any migration ability.
I would just back everything up to an external drive; create the array and copy everything back afterwards
Great, thanks for the info. So now I just need to figure out how to backup 1 T worth of data without breaking the bank.