The Parallels application must be installed on your boot drive. "No choice" to quote you. The VM can be on any drive you like. Just copy the VM folder wherever you like, start Parallels, navigate to wherever you put it, and open it. If you have several physical drives, you can scatter .hdd files all over your machine, point to them in your VM definition, and have the advantage of multiple spindles.
BTW, posting again after an hour makes it seem as if you think we're all here sitting at our screens just waiting for you to ask a question. Let me assure you that that isn't the case. We answer questions in spare minutes when we get a chance, and we aren't getting paid for helping you. A little patience would be polite.
Last edited: Sep 21, 2006