How can I stop my download speed from dropping when I have 2 monitors?

I got my LCD HDTV to connect to my ATI Radeon 4550 graphics card using HDMI so as to have a second monitor to use for my computer. For some reason beyond my comprehension, when I enable the monitors to Extend the desktop my download speed drops ridiculously (to about 0.01 Mb/s from 12ish Mb/s). However, when I disable the new TV, it goes back to normal. Any way to stop the download speed drop from happening?