please help us in getting information regarding working of internet browsers(in general IE or Mozilla etc)....
API's involved..
we want to develop a server tool that monitors and logs the users internet activity such as sites visited, on client machines in LAN.

we're not going to help you create spyware.
If you are legitimate you already have access to the data and all you need to do is find a way to parse the firewall logs.
If you're not legitimate what you're trying to do is a criminal offense.

we are legitimate to this b'coz we are doing it as a part of our academic project.
The project aims at developing a tool for the administrator to monitor the students internet activity and take necessary actions such as banning certain sites.
so would u please tell us the classes or components in java that can help us extract the URL from the browser or how to parse the firewall log?

Google is your friend, we don't do your homework for you! We are here to answer questions about bugs or design patterns

seems the kid is oblivious about the difference between Java and Javascript and/or the difference between serverside and clientside code as well as expecting other to do its homework for it.