Here's an idea. The test site from Cnet to you may be transatlantic and far away. See if you can find a local speed test.
I am on BT Broadband 1.1mbps but the CNet meter test shows my connection speed as 479kbps. Why would this be?
I have a Zoom ADSL USB modem which is capable of 8mbps and a AMD Athlon 2200+, 512 RAM, 120gb HD running XP Home.