I would use Virtual Box for the early distros - e.g. the beta versions. It is the approach that gives you the least trouble. If you don't like it or want to change it, you only have to delete 2 folders.
I have done that with the Win7 Beta and it worked like a charm. It was not even much slower - just a bit.
Else I would subscribe to the advice that Ted gave. With 4 primary partitions you are stuck right now.