Replacement for cookies

Hi

I have a page with a simple competition on it, and only allow users to access the page once and enter the competition once, this is very simple with the use of cookies, but if the user then clears cookies they can then enter the comp again, I would like a few pointers as to how I could implement the use of a flat text file which could log users and then check them against this file.

The users will already be logged into the site, having joined using a .htaccess method of security.

I also have no access to any other form of database.

Any help would be greatly appreciated

John