UMet is a Windows 7/Vista gadget for monitoring usage of your bandwidth allowance. How to use and blog posts can be found at http://umet123.blogspot.com.au/.
You can install the gadget by downloading and running https://github.com/RhinoLance/NetUsage/blob/master/build/NetUsage.gadget?raw=true
Origionally developed for Internode, support for other ISPs can be easily added. Simply replicate the src/Internode.js class, creating the same methods for your own ISP
I am no longer with Internode, nor do I have a Windows 7 computer. As such I'm not actively maintaining this project. Feel free to fork and submit pull requests.
In order to build the gadget, simply zip the contents of the src folder (not the src folder itself), and rename the zip file NetUsage.gadget. That's all there is too it.