[From Gizmo's Tech Tips]
Networx is a useful utility for Windows which tracks your network usage. You can monitor any network connection available on your PC, including wired, wifi and cellular. And you can track by user too. Plus, you can view all the data in a series of pretty graphs and tables, or export it to Excel for later analysis.
Networx is free (strictly donationware), and available in both 32- and 64-bit versions. It's also available as a portable program, for easy installation (there isn't any) and removal.
Link to NetWorx Website