Theme

In drupal 6, the variable $result is available in search-result.tpl.php.  The commented section at the top of this file makes no mention of this variable, so if you want to do something as simple as showing the created date on a node instead of the modified date, then you're in for a bit of researching (unless you read this blog post!).
 
So, if you want to modify how search results are displayed, then you need to:
1) Copy search-results.tpl.php and search-result.tpl.php from /modules/search to your theme's folder.

I recently discovered the Contemplate (Content Template) modules for Drupal. Wow, is it ever a handy little module. Contemplate allows you to create php templates for specific node types. You can create a template for one or all of the following : Body, Teaser, RSS. The great thing about creating node type specific templates in contemplate is that they are theme independent. You no longer have to create a .tpl.php file for that node type in all of the themes that might be in use.