Código PHP:
if (mysql_num_rows($query) > 1){
echo '<select name="titulo" id="tititulo">';
while($row = mysql_fetch_array($query)){
echo '<option value="'.$_SESSION["id"].'='.$row["id"].'">'.$row["titulo"].'</option>';
}
echo '</select>';
echo '<form id="form" name="form" method="post" action="doble.php">
<div class="boton">
<input type="submit" tabindex="11" name="boton" value="Entrar" />
</div>
</form>';