Geeklog Forums

I would like to add the ability for registered users to choose to enter contests on my site. Ideally it would require you to be registered and logged in, then at the click of a submit button, you would be added to a list of some sort for a future drawing. I assume appending to a simple text file with a username/email address per line would suffice. keeping track of weather a user has signed up already during future visits is more complicated though... would that be done via cookies? some entry in the mysql database? my biggest problem is that I don't know PHP so I can't write this myself. Does anyone know of an existing plugin that does something like this?
Thanks for your time!