var isNN = (navigator.appName.indexOf("Netscape")!=-1);

function autoTab(input,len, e) {
	var keyCode = (isNN) ? e.which : e.keyCode; 
	var filter = (isNN) ? [0,8,9] : [0,8,9,16,17,18,37,38,39,40,46];
	if(input.value.length >= len && !containsElement(filter,keyCode)) {
		input.value = input.value.slice(0, len);
		input.form[(getIndex(input)+1) % input.form.length].focus();
	}

	function containsElement(arr, ele) {
	var found = false, index = 0;
    while(!found && index < arr.length)
    if(arr[index] == ele)
    found = true;
    else
    index++;
    return found;
  }

  function getIndex(input) {
    var index = -1, i = 0, found = false;
    while (i < input.form.length && index == -1)
    if (input.form[i] == input)index = i;
    else i++;
    return index;
  }
  return true;
}