Monitor your bandwidth and network usage with PRTG - Paessler Router Traffic Grapher, an easy to use Windows based software solution.
    A very useful tool helps you to receive bandwidth and network usage data that helps to optimize the efficiency of your network. The software is supported with the SNMP, packet sniffing and netflow protocol. This software works with all switches, routers, firewalls, as well as many other network devices. It runs on a Windows machine in your network 24 hours a day, 7 days a week, and constantly monitors and records the network usage parameters. It can even store the recorded data for later reference. It has its own Web Interface and a built in web server to access graphs and tables using any web browser. All graphs are always generated on-the-fly for always up-to-date reporting. It works with most network devices supporting SNMP, and tested with routers and switches from companies like Cisco, HP, 3Com, Linksys and DLink.
    This multipurpose software provides free Paessler SNMP Helper to machines running on Windows 2000, XP or 2003.