This is official release by gamabhana for Drupal 5 module. Download the module from the link present at the end of this post. Extract the contents from zip file after downloading, and then use folder "gamabhana" (and not gamabhana5) for your module.

Same set of instructions specified as for Drupal 6 module can be followed with minute differences in look and feel and other additional settings. This, Drupal 5 module also provides rich text editor.