LinuxQuestions.org - Network Monitoring Software

I have a smal LAN setup for 5 roomates. I'm the only CS major in the house so apparently I am the admin (lucky me) My roomates and I all use filesharing software at different points during the day and I would like to know if there was a program for linux that I could use to monitor the network. I would like to be able to monitor how much bandwidth a certain box is using and what connections are being made that are consuming that bandwidth. Is there a program for linux that would accomplish this?