Hello Venkatesh,
I am not familiar at all with AE LDAP so I am not sure how you would use it and what kind drivers etc. you may need for it, but I have recently looked at ldap as part of a project and have worked with OpenLDAP, ApacheDS and Red Hat's Directory server to an extent.
Since you are a
java programmer??? I would suggest that you get ApacheDS
http://directory.apache.org/ it is a java based implementation of the LDAP protocol plus a bunch of other directory services. It is open source and the developers are really helpful and will give you guidence as to where to find stuff. Here are some links for you:
JNDI
http://java.sun.com/products/jndi/ - you will find some tutorials (
http://java.sun.com/products/jndi/tutorial/) that are really nice here.
Also do a google search for ldap and java and
you should get some good links.
Regards