pam_auth_radius - Map radius user to local account?

Greetings, I have several Linux and BSD servers that I would like to authenticate against my FreeRADIUS server. My question is, do I have to create unix users on each server that match the names of the radius user that I am logging as? For example, could users logging in via radius be automatically "mapped" to a single unix account, no matter what RADIUS credentials they used? Or maybe give users a different unix account depending on the LDAP group they are in? If anyone can point me in the right direction that'd be great. Or if I, in fact, do not want to do this, please let me know. =) --CJ