Just for kicks we attempted this today while trouble shooting some funk with Internet Explorer 6. I know it might sound stupid, but it would be really handy to run a test VM with the older OS supporting IE6 in the MS VM while running the Parallels environment on our Macs. We get an error from MS VM reporting that it thinks the Parallels VM is running a CPU below the minimum of a Pentium II. Not a huge deal if we do not get it to work, but kind of a cool little challenge to wrestle with in our occasional free time.
