function cguestbook() { 
  document.getElementById("submitter").disabled = true

  if (document.getElementById("naam").value == "") {
    alert("Dein Name fehlt")
    document.getElementById("naam").focus();
    document.getElementById("submitter").disabled = false;
    return false}
  if (document.getElementById("email").value == "") {
    alert("Deine E-mail fehlt")
    document.getElementById("email").focus();
    document.getElementById("submitter").disabled = false;
    return false}
  if (document.getElementById("email").value.indexOf('.', 0) == -1) {
    alert("Deine E-mail fehlt")
    document.getElementById("email").focus();
    document.getElementById("submitter").disabled = false;
    return false}
  if (document.getElementById("email").value.indexOf('@', 0) == -1) {
    alert("Deine E-mail fehlt")
    document.getElementById("email").focus();
    document.getElementById("submitter").disabled = false;
    return false}
  if (document.getElementById("tekst").value == "") {
    alert("Deine Nachricht fehlt.")
    document.getElementById("tekst").focus();
    document.getElementById("submitter").disabled = false;
    return false}
  if (document.getElementById("security_code").value == "") {
    alert("Der Sicherheitscode fehlt")
    document.getElementById("security_code").focus();
    document.getElementById("submitter").disabled = false;
    return false}
  else {
    document.getElementById("submitter").disabled = false;
	return true
  }
}


if (navigator.appVersion.indexOf("2.") != -1){
	check = false;
	}
if ((navigator.appVersion.indexOf("3.") != -1) && (navigator.appName.indexOf("Explorer") != -1)){
	check = false;
	}
else {
	check = true;
	}
if (check == true){
	left = new Image();
	left.src = "/images/arrow_left_light.png";
	lefton = new Image();
	lefton.src = "/images/arrow_left_dark.png";
	
	right = new Image();
	right.src = "/images/arrow_right_light.png";
	righton = new Image();
	righton.src = "/images/arrow_right_dark.png";
}

imageStay = ""

function imageon(name){
	if (imageStay != name){
        	document[name].src = eval(name + ".src");
	}
}
function imageoff(name){
	if (imageStay != name){
        	document[name].src = eval(name + "on.src");
	}
}

function light(name){
        if (check == true){
	imageon(name);
	}
}
function dark(name){
        if (check == true){
	imageoff(name);
	}
}