Are you by any chance using component out to the TV, rather than S-Video? I was trying to connect my TV to my PC using a component adapter on my Radeon 9800, and while the picture was undeniably sharp, it caused huge underscan problems like you described, where the top and bottom of the screen were cut off. I eventually gave up on component output and just went back to s-video, because the ATI catalyst control center lets you adjust overscan and underscan if you're using S-video (or a TV capable of the resolutions 1080i, 720p, or higher). The S-video is not nearly as sharp as component (or a real arcade monitor, for that matter), but it's at least better than losing half the image to overscan.
If you were using an ATI graphics card with S-video, I'd suggest adjusting overscan from the Catalyst Control Center. However, you're using an Nvidia, so I'm not sure how you'd adjust the settings for that. Still, overscan is the term you should be researching to solve the problem.