One of the biggest problems in maintaining a healthy LAN network is finding out what your local bandwidth is doing. Sometimes an annoying user using proxies can bypass your firewalls and other 'preventive' counter-measures and allow them to do annoying things like download things or chat.

A great tool for helping visualize this is NetLimiter. This nifty tool is really useful in spotting open ports and the amount of bandwidth a particular IP is using. There are other, better software, but this is cheap and I have found it pretty accurate in spotting anomalies.

Give it a try. The Lite version is free, and allows you to monitor your network. The Pro version allows you to manually set the badnwidth and close ports remotely.

Grab it, and give it a try. Let me know how you found it.