Vantage 3.0 and 4.0 on same machine

We are still using 3.0 but I would like to install 4.0 on a few selected
machines so we can start testing, converting reports and forms, etc. I
remember this discussion before, but can't seem to locate it in any of my
saved messages. What is necessary to do this? If memory serves me
correctly, you need to uninstall 3.0, install 4.0, then reinstall 3.0 for
them both to work.