Network analysis software

[Rory Campbell-Lange]

Hi - please forgive me for a non powerpc question!
I'm looking for Linux network analysis software for our little company
which has a flat LAN with about 100 users running on Ethernet and Bay
switches. Is there anything I should have a look at?
Thanks for any help
Rory 
--
        Rory Campbell-Lange
        The Campbell-Lange Workshop
        London