Need some suggestions about Ns simulator

[Dhanant Subhadrabandhu <dan@ctr.columbia.edu>]

       Dear All,
            I am Mr.Dhanant Subhadrabandhu, graduate student in Columbia
       University. Now I am studying Ns Simulator and try to apply it with
       some simple scenario which shown below,

                    -----
       Source 1 -----   |
                        |
       Source 2 -----   |----------------------- Sink
                        |
       Source 3 -----   |
                   -----|
  
                  (FIFO queue)

        I just want to collect some statistics such as Packet arrivals and
        Buffer lenght.  Unfortunately, I don't know how to start modifying
        this simulator for my purpose. I know that you are very busy and
        have a lot of thing to do but could you give me some suggestion
        about what file I should concern and modify them for my objective.
        And I have to create my own Tcl file or not. Your suggestions is
        very much profitable for me.

        I am waiting for your reply. Thank you very much for your time and
        concern.

        Sincerely yours,
        Dhanant Subhadrabandhu