For anyone who wants to try Zimbra without installing it on their current live system you can now get VMWare Server completely free (and legally).
VMWare have made VMWare Server free and it can be downloaded here. You can even get a copy of a prebuilt Linux system from Red Hat, Novell & Ubuntu - very handy for testing Zimbra. Be aware that this type of configuration will strain the resources of any PC but if you have a fast PC, plenty of disk space and lots of RAM it is useful for testing.
There's also a range of community built Virtual Machines available here You should also be aware that this is a beta program and as far as I can see there's no catches - if you find any please point them out.
Please note that there's currently a problem getting these downloads, on the registration page you must enter a US State and a zip code (even if you're outside the USA) to be able to register correctly and allow you to login. The wonders of modern technology, hey?