Using OS X Mountain Lion Server and a Leopard Client I have a Mountain Lion Server I just got to play with (learn server).  I understand I can use it for Open Directory services.  I believe I can migrate users off their laptops onto the server, and sync'ing (I forget the name, but it makes the user account available on whatever mac they use that is connected to the domain).

1) Do I migrate the users off laptops and on to the server using migration assistant?

2) Can my sons laptop play too?  He uses a G4 iBook running Leopard.
1) Yes, I was able to use Migration Assistant to move accounts off of laptops and on to the server.

2) In using Migration assistant the profile on my sons laptop was "upgraded" to a 10.8 (Intel) version.  This profile was incompatible with Leopard.  So no, my sons laptop was not able to use this system.