may be more ways to skin a cat but heres some
if you go to admin interface and click on downloads and like go to download the pst import wizard, it's always tagged with the current version.
on the server as root you can normally query your package manager and see what versions you have installed of the zimbra packages. like i'm on suse which uses rpm so i can do
Code:
castor:~ # rpm -qa | grep zimbra
zimbra-mta-5.0.21_GA_3150.SLES10_64-20091212003413