Wordpress Themes - WP Forum at BFA - Category search question....

Howdy. I have a category search on the Home page of my site shackn.com. It uses the following code:

Code:

<form action="<?php bloginfo('url'); ?>" method="get">

 <?php wp_dropdown_categories('hierarchical=1'); ?>

 <input type="submit" name="submit" value="view" />

 </form>

In relation to the way I write posts and assign them to specific categories, my technique is as follows:

*Every post is assigned a location from the children of "Location" category.
*Every post is ALSO assigned to EITHER the "Accommodation" or "Surfbreaks" category.

On the "Results page", after the user selects from the drop-down list on the homepage and presses "Submit", I would like the results of this search, to only display posts from only the "Surfbreaks" category, but not the "Accommodation" category as well.

Any ideas how do I do this?