Hi
You can use Webmin for stuff like PostgreSQL Admin.
Let the SME Server Manager take care of Apache, Samba, DNS (No Bind!), DHCP, Firewalling, Hardware and stuff it can handle.
Use Webmin for anything "extra" like PostgreSQL, or even Stuff like MySQL, included and used in SME, but without much options (any?) in Server-Manager.
YMMV
Andy Wismer