Custom Drupal 6.4 module

I need some functionality added to Drupal 6.4, but I don't have time to come up to speed on how to do this. I'd like to do this with as minimal work as necessary. I'm unsure whether this requires a module, or if this can be done with something smaller. I'm looking mainly for features, not content. I can add the content as long as the framework is there. I need the following function: * Visitors to the website who are not registered users who visit a particular menu item need to see a page saying that they'll need to register to access this feature. * Registered users who have not yet successfully used this page will get some text they should read and an action button that they can press. When the button is pressed, their user name and email will be urlencoded on the server side and added to an HTTP GET URL fetched from a backend server. That HTTP GET request will return a code string. That code string should be stored in Drupal user profile storage and the page in the next bullet item displayed. * If the above is successfully completed, or if a user revisits the page after it's already been done, the some surrounding text and the code string stored in the user profile should be displayed. If this can be done with a single custom PHP page, that would be great. I'd consider a minimal module if that's required to add the user profile storage.