OMG, how could all those unix networks exist without GPOS so long!
(for some things you can use samba)
check out what Suse or Redhat can offer.
thy sell server and desktop editions, I am sure they have something to solve your needs
and no one says that Linux has to cost nothing
an other thing you can think about is, possible you should not try to copy/emulate the windows way of solving things with the Linux/Unix environment because for a comparison the result will be not that valuable.
so before calling something shit you should possible find out how people work with the tools they use. maybe you find out that GPOS like in Windows are not always needed.
and of course (
) you should use Slackware or something base on Slackware like http://www.microlinux.fr
central authentication is from time to time a topic in the Slackware forum
there have been recently discussions about central authentication, PAM and so on and there are people that said that is not required at all, so if you want to have some interesting discussions ... :-)