Why would you need MADS when all of your Servers are SAMBA?
You can join a Win 2K3/2K servers to a samba domain, easy peasy.
You can manage them with MMC just like you could before. You just can't use MMC with the SAMBA Domain (for that SRVTOOLS are needed)
Since you can do ~ 90% of the stuff in AD with a DOMAIN you might wanna consider going without AD.
You can get the Kerberos to issue proper tickets and have LDAP do the replication stuff. Amoung other things.