Motherboard: Gigabyte GA-870A-UD3. CPU: AMD Phenom II X6 1090T 3.2GHz. Present graphics card: AMD Radeon HD 6850 1GB PCI Express, with no HDMI out port. Power supply: 700W. Operating system: Windows 7 Home Premium 64-Bit. Want to surf web and stream movies from pc to HDTV (not a gamer or graphics pro)
You have 2-d PCIEx16 running x4 so you can pick ANY AMD HDXXXX with HDMI output and just add it in there.
You then be able to connect it to the TV and use it for what you need as extended desktop - you can manage you both cards from ATI Control Center.
Some cards will pass audio over DVI using a DVI to HDMI converter cable. I know some 6850s are able to do this, so if you know the exact model of your card you might want to google it and see if it is possible. You may only need to buy a cable.