<?    

if ($_POST["submit"])    
{    
    $items = explode(",", $_POST["textfield"]);         

    echo "<form name=\"form\" method=\"post\" action=\"$_SERVER[PHP_SELF]\">"; 
    echo "<input type=\"text\" name=\"textfield\"><br>"; 
    echo "<select name=\"opties\">"; 

    for ($i = 0; $i < count($items); $i++)    
    {    
         echo "<option value=\"$items[$i]\">$items[$i]</option>";   
    }    

    echo "</select><br>"; 
    echo "<input type=\"submit\" name=\"submit\" value=\"submit\">"; 
    echo "</form>";    
}    
else    
{    
    echo "<form name=\"form\" method=\"post\" action=\"$_SERVER[PHP_SELF]\">"; 
    echo "<input type=\"text\" name=\"textfield\"><br>"; 
    echo "<input type=\"submit\" name=\"submit\" value=\"submit\">"; 
    echo "</form>"; 
}    

?> 