Your connection is 100 Base-T. But you get the speed provided by your provider. The 100 MB/s is available on your LAN/Ethernet card, but your actual speed is determined by your ISP. There are utilities available to tell you the actual speed, you can do a Google search for them. Broadband Reports.com http://www.broadbandreports.com/ may have some utilities.
I live in India and I subscribed for a 256k broadband connection recently. But when I connect to the internet, it shows the connection speed as 100Mbps. How is it possible ?