Migrating from a 10.4 (Tiger) to a 10.7 (Lion) Server. What should I know?

I'm the only technician at my workplace that dabbles in Apple devices (we are invested heavily in a Microsoft environment, and Exchange servers work for most of our clients). Recently, one of our clients that is dependent on a Mac-environment got a new server (10.7).

I've been trying any articles on migrating to a new server, but have been able to find nothing on a 10.4 to 10.7 migration. Will I be able to migrate their mail server and file server settings or will it be more viable to just set up the server as new and manually migrate the data afterward? Also, are there any significant changes I should be aware of between 10.4 and 10.7, from an administrative standpoint, or are they roughly the same thing with some new bells and whistles?