//credit: www.youngpup.net
function validateForm() {

	var f = document.nieuwsbrief;
	var i = 0;
	var errors = [];

	// Bill-to section

	if (f.__naam.value == "")	
		errors[i++] = "Naam";
	//if (f.__bedrijfsnaam.value == "")	
	//	errors[i++] = "Uw bedrijfsnaam.";
	//if (f.__pc.value == "")	
	//	errors[i++] = "Uw postcodecijfers.";
	//if (f.__pc2.value == "")	
	//	errors[i++] = "Uw postcodeletters.";
	//if (f.__huisnummer.value == "")	
	//	errors[i++] = "Uw huisnummer.";
	//var __tel = f.nettel.value+f.telefoon.value
	//if (!isValidTel(__tel))
	//	errors[i++] = "Uw telefoonnummer.";
	//if (f.__straat.value == "")	
	//	errors[i++] = "Uw straat.";
	//if (f.__woonplaats.value == "")	
	//	errors[i++] = "Uw woonplaats.";
	if (!validEmail(f.__email.value))
		errors[i++] = "Vul een geldig e-mail adres in.";

			
	if (errors.length > 0) {
		alert(STD_ERROR_PREFIX)
		return false;
	}
	return true;
}

// as convenient a place as any to store this...
var STD_ERROR_PREFIX = "Wilt je zo vriendelijk zijn om Naam en E-mail in te vullen:\n\n"

<!--- Email validation with Regular Expressions --->
<!--- SOURCE: http://www.webreference.com/js/column5/ --->
<!--- Edited by: Bert Votsis (bert@votsis.com) --->
<!--- comma's and spaces are now also non-valid characters --->
function validEmail(str) {
  // are regular expressions supported?
  var supported = 0;
  if (window.RegExp) {
	var tempStr = "a";
	var tempReg = new RegExp(tempStr);
	if (tempReg.test(tempStr)) supported = 1;
  }
  if (!supported)
	return (str.indexOf(".") > 1) && (str.indexOf("@") > 0);
  var reg1 = /(@.*@)|(\.\.)|(\ )|(\,)|(@\.)|(\.@)|(^\.)/; // not valid
  var reg2 = /^.+\@(\[?)[a-zA-Z0-9\-\.]+\.([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/; // valid
  return (!reg1.test(str) && reg2.test(str));
}
function isValidTel(s) {
	var reg = /^0\d{9}$/;
	return reg.test(s);
}

//credit: http://mobile.lycos.nl/mobile/
if (navigator.appName.indexOf("Netscape") >= 0 &&
	parseInt(navigator.appVersion) >= 4) { var nn4 = true }

//document.registerForm.__event.onkeydown = countChars;
if (nn4) document.captureEvents(Event.KEYDOWN);