Filter search results based on meta

Hi I am trying to filter a search based on it having 2 sets of meta

So the search would be:

1.Keyword
2.Meta Value 1
3.Meta Value 2

The end user would put in keyword and then select the meta values from a drop down box queried from the database which I already have worked out how to do:

<form name="search" action="" method="get">
  <select name="option">
  <?php
  $metakey = 'option';
  $options = $wpdb->get_col($wpdb->prepare("SELECT DISTINCT meta_value FROM $wpdb->postmeta WHERE meta_key = %s ORDER BY meta_value ASC", $metakey) );
  if ($options) {
    foreach ($options as $option) {
      echo "<option value=\"" . $option . "\">" . $option . "</option>";
    }
  }
  ?>

And then submit and the search would be filtered by keyword and if it had meta from Meta Value 1 and 2.

Any ideas on how I might get this to work?

Thanks.