Has anyone heard of ntop? It's a tool for 'snooping' on your network traffic that was recently featured over at TechRepublic. Ntop gives you information on "network load throughput, active connections, which hosts are connecting to what sites, the amount of bandwidth sent to a particular site, protocol usage, and more."
For ntop to be effective (due to the way routers and hubs work these days) it would really need to
be installed on a number of machines in your network so you can see a more complete view of
Free is my favorite price. What a great birthday present.