function registerUser()
  {
    var ok = true;
    $("surname_x").hide();
    $("lastname_x").hide();
    $("city_x").hide();
    $("emailaddr_x").hide();
    $("img_warning_fld_home").hide();

    var surname = $("surname").value;
    var lastname = $("lastname").value;
    var city = $("city").value;
    var emailaddr = $("emailaddr").value;

    if( surname == null || surname.length < 2 )
    {
      ok = false;
      $("surname_x").show();
    }
    if( lastname == null || lastname.length < 2 )
    {
      ok = false;
      $("lastname_x").show();
    }
    if( city == null || city.length < 2 )
    {
      ok = false;
      $("city_x").show();
    }

    emailreg = new RegExp(/^(("[\w-\s]+")|([\w-]+(?:\.[\w-]+)*)|("[\w-\s]+")([\w-]+(?:\.[\w-]+)*))(@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$)|(@\[?((25[0-5]\.|2[0-4][0-9]\.|1[0-9]{2}\.|[0-9]{1,2}\.))((25[0-5]|2[0-4][0-9]|1[0-9]{2}|[0-9]{1,2})\.){2}(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[0-9]{1,2})\]?$)/i);
    if( emailaddr == null || emailreg.test( emailaddr ) == false )
    {
      ok = false;
      $("emailaddr_x").show();
    }

    if( ok )
    {
      // Ajax
      $('registerdiv').hide();
      $('loadingdiv').show();
      registerUserAjax( surname, lastname, city, emailaddr );
    }
    else $( "img_warning_fld_home" ).show();

    return true;
  }
  function registerUserAjax( surname, lastname, city, emailaddr )
  {
    var ajax = new Ajax.Request( 'ajax.php?r=registreren&surname='+surname+'&lastname='+lastname+'&city='+city+'&emailaddr='+emailaddr,
      {method: 'post', evalScripts: false, parameters: '', onComplete: registerUserHandler }
    );
  }
  function registerUserHandler( xhr )
  {
    $('registerdiv').innerHTML = xhr.responseText;
    $('loadingdiv').hide();
    $('registerdiv').show();
  }