Help with Forms

Hi, I need to create a page with some form elements where a user can register their computer system. One of the fields needs to be executed with a .exe which will return a serial key. I can run the .exe at the command line like "name.exe arg0" and it will print a serial key which I want to be able to display. I also need to write the users name (I make them give one at registration using the profiles module - profile_first_name) and the form results to a file. Lastly I want to be able to list all the systems that the user has registered already and give them the choice to remove them individually. Any help would be appreciated I don't really know where to start, I've just created an html page with no php functionality yet. (also where should I place the php file so drupal knows where it is after I submit the page as a node)