Macbook as Tv Output?

I have not got a clue about how this would work, if it would at all.

Say I wanted to play a games console and use my macbook's screen as the output instead of a standard television?

Thanks for any help you can give.

You can't do it.

Actually, you CAN do it, but it's not free

The Macbook doesn't come standard with video-in, only video-out. In order to input video, you're going to have to get an external tuner card. Elgato has some Mac models, and I'm sure there are others. This particular model offers the ability to plug in a game console:

eyeTV 250

You will need a decent processor, I'm not very sure wether experience will be smooth on a Macbook. The no-latency mode in EyeTV is not bad, but it could be better.