I currently have a desktop computer and want to use my big screen tv across the room as my monitor so I can use it as the main monitor. What exactly is it that I need to accomplish this?
This is what I do, but also have 2 desktop computers connected as well. You need to look at the back of your video card and match up the connections to your tv. VGA is fine for just using it for documents and stuff, DVI/HDMI is whats required if you plan on watching movies/video. It might require a new video card. You can get long 30'+ cable on the cheap from Monoprice. Report back with your video card model (or what kind of outputs you have on it) and your available inputs on the back of your tv.
I assume your going to want sound so you'll need to pick up an adapter for that. You will probably either want to pickup some type of remote control or longer range mouse. As mentioned above your going to need to match the output on the video card to the tv. There are adapters that you can buy as well if changes to the hardware isn't something your into. What operating system are you using?