What type of networking? Samba, LDAP, NFS?
I would suggest CentOS if you are looking for eventually getting a Linux job. It's a clone of Red Hat Enterprise Linux, which is most common in enterprise environments.
Otherwise, I'd recommend Debian or Slackware. Both of them allow you to get to the basics of Linux, without a lot of the overlays that other distros provide.
I started with Slackware and, if I had to narrow the recommendation to one distro, Slackware would be it. Once you get it installed, you have a full distro and all the tools you need for day to day computing, but, when you start to configure it, it doesn't hold your hand and it is a damned good teacher.
If you learn what you want to learn in Slackware, no other distro will ever intimidate you.