What you are experiencing is common when connecting a PC to an HDTV. You need to go into your video card control panel (like Radeon's Catalyst Control Center), look for something similar to "HDTV Scaling". Typically adjusting it to 100% should resolve the issue.
My LG 47LH90 has an Aspect Ratio option called "Just Scan" which was a simple fix for my issue.
I believe all LCD HDTV starting at 32" and all Plasma HDTV starting at 46" are 1920 x 1080.