combo box problem

i want when value change on my combo box it display the corresponding web site in new tab or window

<?
function  managelinks_block($op = 'list', $delta = 0, $edit = array()) 
{  
if ($op == "list")
 {
    // Generate listing of blocks from this module, for the admin/block page
    $block = array();
    $block[0]["info"] = t('Select a link');
    return $block;
  } 
else if ($op == 'view') 
{
   $query = "SELECT title FROM " .
     "{managelinks }";

  $queryResult =  db_query($query);


  $block_content = '';  
  $cbo ='';
 
  while ($links = db_fetch_object($queryResult)) 
  {   
   $option[] = $links ;
  }
  
  $cbo .= '<select onchange="address(this)"  name="select" id="select">'; 	
  
  foreach( $option as $key => $val)	
  {		
  $cbo .="<option>".$val->title."</option>";
  } 
  $cbo .= '</select>'; 	
  
  
  $block_content .= $cbo;
  $block_content .="<input type='submit' value='Go'>";
  
  ?>
  <script>
    function address(obj)
		{
		var dropdownIndex = document.getElementById('select').selectedIndex;
		var dropdownValue = document.getElementById('select')[dropdownIndex].text;
		//alert(dropdownValue);
		<?
		$query = "SELECT url FROM " .
        "{managelinks } where title='dropdownValue'";

		$queryResult =  db_query($query);
 
		while ($arr = db_fetch_object($queryResult)) 
		{   
		?>
		alert("$arr[0]");
		document.forms[0].cat_name.value= obj.options[obj.selectedIndex].text;
		<?
		}
		?>
	</script>
  <?
  
if ($block_content == '') {    
    /* No content from a week ago.  If we return nothing, the block   
     * doesn't show, which is what we want. 
     */
    return;
  }

  // set up the block  
  $block = array();
  $block['subject'] = 'Manage Links';  
  $block['content'] = $block_content;
  return $block;
}

  


} // end function 

?>

but it doesont work well,so any help

thanks for advance