samba - Jul 1999 - Fault Tolerant Configuration

I've set up a Samba PDC serving 100 users, and various other services on
the system.  It serves 100 users, and we've had very few problems with
it.  

However, what kind of options are there in case the PDC goes down?  Is
the BDC controller support there yet?  What kind of system can i devise
to have the least downtime if the main server were to go down.  This
includes keeping the data in sync, etc.?  Are there any solutions as far
as that?

Thanks,

Ben