Try adding the following code to the top of your search.php template below the get_header() call:
<?php
global $query_string;
$query_args = explode("&", $query_string);
$search_query = array();
foreach($query_args as $key => $string) {
$query_split = explode("=", $string);
$search_query[$query_split[0]] = urldecode($query_split[1]);
} // foreach
$search = new WP_Query($search_query);
?>