Making an email form dynamic?

I've now uploaded a working version of what I want to achieve but it's not the slickest of ways I don't believe. I use a jump menu form to put a value to orgname in the url. The main form then sits below and the class (categories in the code!) options (it's the riders skill and bike size) gets filtered by the orgname. It's stops a registrant from selecting an organisation/class combination that doesn't exist. I think it's a bit agricultural to use to use two forms and $_GET to achieve this though..The select statement is this:

mysql_select_db($database_connPitlane, $connPitlane);
$query_rsClassregister = sprintf("SELECT catID, catname FROM categories WHERE categories.catorganisation=%s ORDER BY catID ASC ", GetSQLValueString($varClassregister_rsClassregister, "text"));
$rsClassregister = mysql_query($query_rsClassregister, $connPitlane) or die(mysql_error());
$row_rsClassregister = mysql_fetch_assoc($rsClassregister);
$totalRows_rsClassregister = mysql_num_rows($rsClassregister);

and the html in the form snippet is this:

<label>Class</label>
    <select name="FieldData2" class="setwidth">
      <?php do { ?>
      <option value="<?php echo $row_rsClassregister['catname']; ?>"><?php echo $row_rsClassregister['catname']; ?></option>
     <?php } while ($row_rsClassregister = mysql_fetch_assoc($rsClassregister)); ?>    
    </select>

Hopefully i've explained it enough but like I say, i'm really just starting out!! :-)

Sounds like a SQL problem. What does your select statement look like?