Welcome to LQ!
Funny you should ask this, as I'm currently tinkering with getting LDAP authentication set up on my home LAN. The software you should be looking for is OpenLDAP, which should be on your distro install CDs or downloadable. if you want to try to build from source, as I did, you can get the sources from www.openldap.org
One big fat word of caution -- configuring LDAP is not easy for someone new to the system. I just spent about 3 hours of solid work/googling/frustration tonight getting to the point where I could have a basic database (of course, I ran into some trouble and had to recompile my Berkeley DB -- the one included with Slack 10 didn't seem to want to work with OpenLDAP). There's a HOWTO at http://www.tldp.org/HOWTO/LDAP-HOWTO
but it doesn't seem to really deal with setting OpenLDAP up for authentication (or very many specifics at all, for that matter). I also found some nice documentation at http://www.zytrax.com/books/ldap/
. Google will definitely be your friend here.
Now that I have my LDAP sort of working, next step will be actually authenticating users off it and actual security... I won't be getting to that until tomorrow or Sunday. Good luck in your endeavors with it!