What are you backing up to, DVD, another disk, tape?

Virtually any backup software can back up the clients, the easiest way is to share their drives and map them from the server, so that server is just backing up a bunch of drives it sees as local drives. That's way easier then messing with clients on the workstations, etc.

It won't get the registries, but as long as you have an export of the registry on each hard drive (something everybody should have anyways) it will have a backup of it that way.