Zazen is a unique form of mediation because one keeps their eyes open while meditating. You keep your eyes focused on a spot on the wall. Everything else is the same as any other type of meditation. I do Zazen about 1x a week for 20 minutes. It helpes one feel more centered and relaxed.
Here's a video by Brad Warner on how to do Zazen. You can also meditate sitting indian style.
http://www.youtube.com/watch?v=dIe7z8HpLEE