This question was asked in debianhelp.org almost half a year ago, but never got an answer. I wasn't the one who posted it, however I was today facing exactly the same question. Not sure if copying it to here as such is considered as inappropriate or something, but there's not really anything that I would even like to paraphrase... So let's just go. (I'm sure you will be happy to close it, if this is not the way to go :)

Hello all! We are using a Bugzilla server install on a Debian 4/Etch server and are starting to look at the upgrade to Debian 5/Lenny. I was hoping to upgrade the existing Bugzilla server and database from the oldstable (v2.22) to the newer stable in Lenny (v3) when we get to doing a dist-upgrade. However from testing in a virtual machine it seems that the old package was called "Bugzilla" whereas the Lenny package is called "Bugzilla3" and I could not figure a way to directly upgrade between the two.

Is it possible to establish some kind of upgrade path quickly after the dist-upgrade to minimise downtime using apt-get or aptitude? Going on past experiences I would not want to do a fresh install with the Bugzilla3 package and attempt to inject the old database into it (previous attempts failed miserably!) :(