Mezo
You can't, or at least shouldn't , put these two devices in any kind of RAID. Period. Such a RAID would be limited to the speed of the HDD, negating the advantage of the SSD, and be limited to the capacity (RAID1) or twice the capacity (RAID0) of the SSD. You would be wasting most of the space on the HDD.
(Note that setting the controller mode to RAID does not put volumes into a RAID set, it just allows you to do so manually.)
The Z68 chipset allows you to use an SSD as an extended cache. Doing this makes the space on the SSD unavailable to you for direct use. If you use it that way, you will have to install your OS on the HDD. Honest.
My Win7 install also runs close to 50 GB, but I'm running a 128 GB SSD.