Internet bandwidth is a precious commodity. In countries like India, broadband access is limited by the amount of data (uploads/downloads) that you can transfer.
You may also want to monitor your internet speeds regularly. Third-party sites can be used for this purpose, but such tests are inaccurate because of latencies and other inefficiencies. The best way would be to install a program in the computer to monitor how much data is sent out and received.
NetMeter is a small Windows utility to monitor your bandwidth usage (total, daily, weekly and monthly). It shows graphical representation of internet speeds, with the internet speeds in numbers and the bandwidth usage in numbers below the graph. The window is resizable and can be docked into any part of the screen. I usually dock it in the bottom right corner.
In Windows XP, NetMeter supports transparency and click-through. There is also fade-in and fade-out transparency, which means that NetMeter will fade away when you hover the mouse over it. Click through feature basically makes NetMeter an overlay, so that you cannot click it (it becomes partially transparent too).
Tip: Right click on NetMeter for a context-menu with Options, Totals log and Show/hide NetMeter.