Sites that give things away for signing up for surveys, etc

How do those sites work that give things away for users performing certain actions?

Like, for instance I run a site dedicated to a certain videogame. I’m getting a good deal of traffic but not getting very far with Adsense. A competitor has something set up on his site where he gives away a free copy of the game each month, and users enter the drawing for the free game by completing a survey, or some kind of trial or something.

I’ve looked high and low for something like this. For instance I get $15 through CJ when someone signs up for a gamefly trial by clicking through a link on my site. However there’s no way to track who exactly has signed up (so I can’t enter them in the drawing).

So how can I set this kind of thing up with getting users to take surveys or sign up for trials in exchange for entries into my drawing?

Ya i would like to know the same how to track people who have signed up using ur afiliate link?