Automatic URL-specific style sheet selector

I am working on a basic theme for a dozen related sites and want to change the style sheet based on the server-name. These are small geographic sites that use the exact same theme. The content is set in the settings.php file Sso they will have a large picture banner similar to the background picture in the marinelli theme. Note that the new marinelli theme actually calls a rotate.php page in the style sheet to select a random picture. Basically I am trying to find out how to set is so that it will work on a site-specific folder or better yet create an alternative style sheet in the theme than will be called based on what the site name is. Using Drupal 5x

Any suggestions much appreciated.