Setting up a new machine with the latest versions of OS and Zenoss is the easiest way to go in my opinion.
With the RPM install, zenoss user is setup automatically and good news it is you don't need to know its password. Just setup sudo so you can change from your user to zenoss using your own password. The RPM setup also installs the scripts for automatic startup of Zenoss, use the chkconfig command as root to make sure it starts at each boot and good old /etc/init.d/zenoss start to run it and be able to access the web interface.
As for database migration, I never did it myself but I believe I saw a post on this forum that talks about it. Search for migration to version 4.2 related posts.