using a cinema display and a DV to and HDMI TV

I have been watching tutorials but haven't been having much luck. I have a 50 inch 1080 HD TV and a late 2009 8 core Mac Pro. I bought a DV to HDMI adapter but can only see the the back ground when I have every thing hooked up. When I try to mirror the displays, I lose my 2560x1008 display on my 30 inch cinema display.

Is there something I am missing to add a second monitor to my 8 core for more real estate, or am I going to have to use the mirror function only and have two displays with the same content?

I was hoping to have more real estate when editing with FCP and Pro Tools.

Cheers.