At a previous job, we had our Mac server configured so that we could log into client machines using any network user account name and the local admin password. I can't seem to find out how this was accomplished, and google isn't turning up anything particularly useful. Does anyone know exactly how to accomplish this?
SnapOverflow
It sounds like you probably had the "Enable administrator to masquerade as any registered user" option set. More info available by Googling this phrase. See point 6 of this document for initial Tiger specific info. I think Leopard is the same, but I have no Leopard Server close by at the moment, so I can't check.
In my Leopard-based Server Admin tool controlling my Tiger server, the option is under the AFP Service section, Settings subsection, Access tab.
Hope that helps.
I would suspect this means that your Mac's were authenticating against some sort of directory service, in your case most likely OSX Open Directory, other options include active directory, open LDAP or other services. This is a centralised directory of user accounts that can be used on any machine in that or organisation.
There is a good article here discussing the concepts of Open Directory. For actual setup instructions, this is a good guide.