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;
}