I have a Mac Pro with two hard drives. One has OS X on it, and one is dedicated to Windows XP (installed using Boot Camp). I tried using Parallels to boot from this hard drive, but I just get the dreaded "Error loading operating system" or "Cannot boot from disk" messages. I put the files in that Driver Cache folder as well, and it still doesn't work. Am I missing something, or does Parallels STILL not support this? I remember trying this right when this feature was first announced over three months ago, but I imagined they would have fixed it by now (or at least added more trouble shooting steps to the manual). I would really appreciate anybody's help on this topic!
Last I heard there was not official support on splitting Parallels across multiple drives. There have been mixed results in getting this to work.