I'm usualy choosing an Disto named IPBrick (http://vmn.pt/ipbrick/indexen.html
) as PDC witch is very user friendly.
It has an WebAdmin to manage almost all features we need in an server.
Recentely I've migradet hundreds of users (usernames, pws, e-mail addresses, etc) from a Windows Server 2003 to IPBrick in seconds, with a csv file exported from Windows and imported to Linux.
Give it a try, but note that it isn't free...
In my oppinion is the best Linux Distro to Sys Admin how want to start working with Linux Servers.
I hope this will help you!
PS - This post is almost the same as in annother Thread, but the question is very similar. Sorry to Forum Administrators.