To all who use Speedguide.net
Those speeds that you get on Speedguide.net are not that accurate. Those tests work by registering how fast your browser reacts to certain conditions. To accurately test your line speeds, check out the line speed test at DSLReports.com. You'll be surprised at how much slower you line really is that your browser.
As for the listing on your cable connection, your modem's ethernet port is 10Mb. All cable modems have a 10Mb ethernet port UNLESS you have a digital cable modem, in which it is 100Mb. Most people do not have digital cable modems. When you look at your speed in Windows XP, that is not your actual line speed, but the speed between your NIC and the next available device (modem).
Most people who use cable internet services on DOCSIS networks get what are known as burst speeds. This is when bandwidth is reallocated from someone who isn't using their bandwidth to someone who needs the extra bandwidth. The result is that some users download files above their bandwidth cap (most cable providers cap your modem at 1.5. Others, like mine, cap it at 2Mb). Even though my cap is at 2Mb, I can download at speeds up to 5Mb because of bursting.