In order to monitor that at the network switch level you’ll need a managed switch such as a cisco catalyst switch or a higher end router. You could setup an ISA server and route all the internet network traffic through that to see who is using the most bandwidth.
If your LinkSys supports any sort of logging that may also give you an idea on who is using the bandwidth.
Keep in mind that 1 Meg of bandwidth for 50 people is not a lot. My office with about 20 people has a 100 Meg link to the Internet. And my house with two people has a 18 Meg network connection. With just a few people doing normal web surfing that 1 Meg connection will fill up pretty quickly.