There is no simply answer, at the lowest common dominator you have the simple login, ssh, or even finely grained ACL’s, remote logins. Then I’m not to sure but you may even be able to get some kind of control using app-armor profiles(You’d have to investigate)
ACL’s also man Access control list - Wikipedia, the free encyclopedia
AppArmor Detail - openSUSE
No true login Samba mounts which iirc will give you some user control. Linux HOWTOs and Tutorials: Suse Linux 10.0, 10.1 openSUSE 10.2, 10.3, 11.0, 11.1
Full blown solutions ndis or ldap, brief examples here NIS : Linux central authentication NIS : Linux central authentication Howto LDAP server - openSUSE
Then are we looking at proxy control/caching/filtering are you having a web server etc… squid/squid guard, then if a website are you using a fall back, who is managing dns, wireless etc etc etc…
You have yet to really map out your network, you have so many questions but first you have to have a plan with which services you wish to serve, then solutions can be given.
I mean you have mail servers is this centralised are you sticking to the ms way then you may find there is only way or you may find that what you hoped for wasn’t so easy therefore mail may become more generic way.
You’ve given no idea of the material you wish to serve to the clients, whether thin or fat with/without shares, backup policy etc etc etc etc … Then we’ve not even touched linux to linux and nfs NFS - openSUSE
Then not to forget sometimes where you pull the solution maybe a push.
And then to really throw a spanner in the works you have virtulisation vmware/xen.
Open up your favourite drawing program
|----- | ------|
Services--- Sever ---Services
|----- | ------|
Google wiki is your friend but first map out the network.
Think you have some research and a little mapping to do before the next round of questions.