I know this is a bit late, but it goes like this:
a) 2 drives > one volume.
b) Install OS. Volume is now bootable
c) Add second volume. First volume is still bootable.
d) Install second OS. Since the first volume is bootable, the OS will add itself to the boot sequence of the previous OS (thus the menu to choose OS. If each disk would have an independent OS, the disk selected to boot would determine OS). To achieve independent disks, you need to disable the other disk in BIOS before installing the other OS. Setting boot order will do nothing.
e) Break the raid. Now you have 2 destroyed drives and a drive with an OS that will not boot because it was never bootable, it just hosted the OS
Your options (well, not yours, since in a week or so you probably already fixed it) are as follow:
* Remove the broken drives and use a Vista disk to repair the already-installed Vista (fixmbr)
* Install Vista over the old one (disk 2)
Well, there's the third drive, moving the drive to another pc, but really, it's broken now, you have to start over.
When installing OSs, remember, the active drive hosts the startup of all installed OSs. Next time disable the other drives.
When moving disks, remember, data you don't have a backup of is data you don't want.
Oh, and this tip is free for you (it wasn't for me): Backups fail when you restore because when you don't restore you don't know they're broken. When migrating data, I have 2 copies at all times. One I restore form and one I never touch. If the primary backup becomes broken, I copy the data over from backup 2 then restore from backup 2. Restoration tools are able to break backups.