Mini modules for Drupal 6.x require two files- a .info file and a .module file. These should generally be placed in a separate directory, for example under sites/all/modules. The .info file is needed for you module to show up on the admin page, while the code you want to add will be in the .module file.
I started a mini project to include some of those in D6. If someone wants to have the D5 version, I'll give you access... Although I'll only support D6 on my end.