Cool. I'm working on something like this to get out by 1.0 (the UberInstaller already does something like this already). There's a couple of things you need to do to get this to work with Drupal. The php file has be named .profile and placed into a dir that has the same name as the .profile inside the drupal profiles dir (e.g. profiles/ubercart/ubercart.profile). Also, the functions you create have to be named (name of .profile file)_function_name() (e.g. ubercart_profile_modules()). After that, running install.php will list your profile as an option on the install page. See more at drupal profiles