PLEASE, HELPMEEEE!!!!!

Hi!,
    I am planning to build tester for LANs, that may show you the traffic in
the network at certain periods of time, like:
    1- Instant traffic.
    2- Last 10 seconds traffic.
    3- Last minute traffic., etc, etc.
    I am interested on knowing how to see when the lan cable is being
used -so at that moment there is traffic over the network- and
the rest of mathematics will be done by the PIC processor I choose.
    So if someone has an idea, please write.

            Thanks.-

      Gabriel Caffese
     UNLP - La Plata
gabrielsdi@iname.com