How to solve Mini DisplayPort to HDMI Overscan problem? (Part of the screen is missing)
There should be an "Underscan" adjustment in display preferences. Open up the Displays in System Preferences. Have a look at your available resolutions. There should be a 720p, 1080i and 1080p, choose whichever is appropriate for your TV, and a slider labelled Underscan should appear. Adjust as necessary to get the picture right on your TV.