function check_housenumber() {

	if (document.forms["registerform"].b_housenumber)
	    var b_housenumber = document.forms["registerform"].b_housenumber.value;
	else
		var b_housenumber = "";
	if (document.forms["registerform"].b_streetname)
	    var b_streetname = document.forms["registerform"].b_streetname.value;
	else
		var b_streetname = "";
//	var b_additional = document.forms["registerform"].b_additional.value;
	if (document.forms["registerform"].s_housenumber)	
		var s_housenumber = document.forms["registerform"].s_housenumber.value;
	else
		var s_housenumber = "";
	if (document.forms["registerform"].s_streetname)
		var s_streetname = document.forms["registerform"].s_streetname.value;
	else
		var s_streetname = "";
//	var s_additional = document.forms["registerform"].s_additional.value;

	var ship2diff = document.getElementById('ship2diff');

	if ((b_housenumber != "" && isNaN(b_housenumber)) || (s_housenumber != "" && isNaN(s_housenumber))) { 
		alert(alert_housenumber); 
		return false;
	}

//	if (b_housenumber != "" && (b_streetname=="" || b_additional=="")) { 
	if (b_housenumber == "" || b_streetname == "") {
		alert(alert_housenumber2);
		return false;
	}

//    if (s_housenumber != "" && (s_streetname=="" || s_additional=="")) {
	  
	 if (ship2diff) {
	     if (ship2diff.checked && (s_housenumber == "" || s_streetname == "")) {
             alert(alert_housenumber2);
             return false;
         }
	}
	

	return true;
}