“role” confusion for smb service

I am having trouble getting smb services set up on Leopard Server. Currently the machine is set up as a stand alone server. However, all users who need smb connectivity are authenticated through LADP (not loacal). Can some one enlighten me as to the purpose of the other role options. Specifically I am wondering if I should be using "domain member". I have no desire to do anything but serve files to my small group of windows users in a mixed lab of macs, pcs, and linux users. If this is the case, who chooses the workgroup (you can tell I am a windows neophyte), me or the University network that I am part of? Thanks