Do I have to remove PHP4 in order to get applications to run with PHP5?
No, PHP4 and 5 can co-exist together. Exactly how easy that is depends on if you’re using the GPL or Pro version of Virtualmin 
With the Pro, you can go into Server Configuration -> PHP Versions, and set which PHP version is the default for any given Virtual Server.
But you can also change the PHP version per-directory, so if you wanted PHP5 running as the default PHP version for your site, but you wanted the app running at /foo to be run with PHP4, you can specify that in there.
-Eric
Well I plan to upgrade to the pro version once I can verify that I can get everything running correctly. So far its been good, but there are a couple things hanging me up. I have posted a lot in the forum, so hopefully they will get solved.
Thanks…
So how do I change the directory to use PHP5 under the GPL. Again, I am plan on buying a full license, but I need to make sure a couple things function correctly first, namely, the new version of Roundcube.
i believe domains switching between php4 and php5 is a VM Pro feature
Cephlon you wont be able to test everything using the GPL version - You will need to upgrade and if you still have trouble then come back here for help.
It’s pointless to ask something you don’t have access to with the GPL version.