LDAP registry page with independent Blog name options

First: My apologies if this is already somewhere on the forum, newby, slack appreciated.

Can someone provide a plug in with some "how to" that allows developing and maintaing an LDAP registry for users and allow the user to name the blog by topic.

I am developing http://www.history-of-surfing.com and want to have blogs as sub directories based on location or area of interest ie

http://www.history-of-surfing.com/ocean-city-nj

This is a similar thread from the WPmu forum

http://mu.wordpress.org/forums/topic.php?id=9919