Now I am no expert but I would say that mixing and matching different drives for RAID is a no go. In particular RAID 0 which you will be aware will make all data currently on the hard drive you intend to use as unusable and you would have to start over.
But even if you accepted that, the disk control software for SSDs is so different than for conventional hard drives that I just can't see how its going to work.
I had SSDs in RAID 0 on this machine I am using now and it kept failing because Vista has no TRIM controls. If you intend to use Windows 7 and even if you get it to work, you can't use Win 7's TRIM controls because of the mismatched pair.
Why not forget RAID and just use the SSD as a boot drive?
I want to install a SSD in my new computer, the computer has 2 500gb drives in RAID0. I want to run my SSD with one of those 500gb drives. how do I do this?