I want that instead of a monitor because it would be a much cheaper solution. But my main question is would it work. All I want to do is play my PC games 120hz in HD. Also, would I need to use a special cable?
You've run into a common misconception here. I didn't know about it myself until I read about it in this forum. 120hz TVs don't take 120hz signals - they take 60hz input from a dvd player (or computer, etc.) and interpolate frames to get 120hz, generally adding input lag in the process. To get true 120hz for PC games, you need a 120hz monitor and either a dual-link DVI or DisplayPort cable. 120hz monitors usually also support active 3d with shutter glasses, but often allow you to use 120hz in 2d mode. However, for that, you should look at your video card and find out if it can push well over 60fps in your games. If not, I wouldn't expect the 120hz to be a significant benefit.
HDTVs (all of them) only accepts 60Hz inputs. The internal electronics creates interpolated (or "in between") frames to double the number of frames that is displayed. So... 60 frames in... 120 frames out. This is basically done to improve video playback smoothness.
Since it takes a little time for the HDTV to create these interpolated frames, playing games in 120Hz mode creates input lag. Therefore, it is generally recommend you set the HDTV to Game Mode or 60Hz.