[support] Custom Advanced Search

I am trying to create a custom search, i.e. one which will only search in certain CCK fields. I believe that hook_search for Drupal 5 is what I need: http://api.drupal.org/api/function/hook_search/5 but when I set this up in my custom module and run a search $op comes through as 'name' but not as 'search'. Yet I am seeing the search results page. Is this expected behavior? If so, can someone explain to me what I am missing because I was expecting $op to be 'search' so I could add my keyword pairs to the search SQL to limit it. Or perhaps this is indeed not the correct approach? Thanks, Fred