I wasn't taught the US kind of dodgeball...the Brit equivalent is much tamer.

The court/equipment
The court is simply any large room that can survive foam balls being hurled around in it. There's usually only one ball, sometimes two if you wanted to up the ante.

The players
No teams. Just a free for all, every man for himself. Most of the time, I played with around 29 other people...mucho funno...

The objective
Get everyone out.

The rules
To get someone out, you hit them below the knees with the ball. Even if you ram the ball into your own shin you are out. If the ball so much as touches a hair below your kneecaps, bye bye.
No kicking the ball, because obviously that will get you out.
The ball is thrown in to the game by anybody who is willing.
Once you are out, that is it. Finito.
Unlike the above (US) rules, you can pick up the ball.

The winner
The winner is the last person left.

I was awesome at this game. Seriously, I rocked. See, our school hall was divided in two with a white line, so if you wanted to stay in for as long as possible you just had to keep in the half which doesn't contain the ball. Of course, nobody at that school liked me that much so I ended up being chased by the people with the ball. What fun.