Enabling Sideboxes on Specific Pages

[ideasgirl]

I tried this but doesn't work:

On catalog/includes/modules/sideboxes/mytemplate/search.php

if ($_GET['main_page'] == 'index')
  $show_search= true;
else {
  $show_search= false;
} 

With that code I tried to show the search box ONLY on the main page, but still showing everywhere. Am I missing something?