Hrm. I'm going to make the assumption that you've used the motherboard's RAID options. Usually this turns all of the SATA ports over to the RAID controller. Ones that aren't in a specific setup are supposed to be just sent as normal. Two things to try. Go into the raid options and see if you have to "add" the other hard drive to a single drive thing. Another would be to rightclick "my computer" and hit manage. Then go to the hard drive options and see if it just didn't assign a drive letter because of something stupid like it isn't formatted.
I got the problem sorted out and it was that stupid thing you mentioned that it didn't assign a drive because it wasn't formatted. Wasted so much time on something so small and stupid that windows 7 should do automatically. Anyway thanks for your response I appreciate your help.