I was searching this tool for several months.Ntop which was available for Linux for one decade is now also available for Windows OS.It is really good tool to track your bandwidth usage on your network.You can find out who is choking your network bandwidth by using unnecessary programs.
It gives real time usage by protocol wise, application wise.Simply keep the software on the perimeter of the network i.e. on the gateway of your network and it will display all the sites being visited by your users in the network sorted by protocol usage.

You can download Ntop for Windows by going to this URL.Installation is fairly simple.Just download the exe and run it.Complete the installation and you will get a Commander program in your Windows programs list.Run the commander, from here you will be able to start Ntop service and launch the ntop interface window.By default it uses port 3000.You can also type the IP address of the pc along with the port number 3000 to see the Ntop data.The address will be http://your-ip-address:3000 , here put the ip address on which the Ntop is installed and
you will get Ntop interface.

Now all the hassles are gone for administering your network.Just use Ntop and MRTG for Windows or Linux and play wise.