Upgrading from Panther to Tiger Server – hints?

We’ve got an existing installation of 10.3.9 Server on an Xserve and are considering moving to Tiger Server at the end of the year. I was wondering if anyone had any helpful tips on that migration. Does it run an archive and install like the clients do, should I backup our existing 10.3.9 to a seperate hard disk (I will anyway) and use migration assistant (does tiger even have this on the server edition) to move everything over, or is there a completely different routine that I should follow for upgrading. Any help would be greatly appreciated as I want to avoid downtime as much as possible.