Uninstall/Reinstall of //3.0 and Vista under OSX

Config: Mac OX 10.4, Parallels 3.0 Mac, Vista Ultimate on MBP 2.4 Ghz

I've read several approaches for access for multiple users to //3.0

I've decided simplest is to create a new separate user account primarily dedicated to accessing Vista. Problem is I've already loaded Vista under another user.

Unfortunately, I believe I must uninstall //3.0 and Vista then reinstall both under new user account.

1. Is this assumption correct?

2. I know how to uninstall //3.0, does install of // uninstall Vista also because Vista is no longer accessible? Or do I need to uninstall Vista also. If so how does one do that (wipe disk?) Or will reinstall of // look for/find existing Vista install

thanks in advance for any helpful direction....