function openWindow(url, height, width, name) 
	{
	   var left = Math.floor( (screen.width - width) / 2);
	   var top = Math.floor( (screen.height - height) / 2);   
	   var winParms = "top=" + top + ",left=" + left + ",height=" + height + ",width=" + width;
	   winParms += ",status=no,toolbar=no,menubar=no,location=no,scrollbars=no"; 
	   var win = window.open(url, name, winParms);
	   if (parseInt(navigator.appVersion) >= 4) { win.window.focus(); }
	   return win;
	}



function SubmitForm()
	{
		var sError = "";
		var bReturn = true;
				
		if (document.frmGastenboek.message.value == ""){sError = sError + "- Uw bericht\n"; bReturn = false;}
		if (document.frmGastenboek.user.value == ""){sError = sError + "- Uw naam\n"; bReturn = false;}
			
		if (sError == "")
		{
			document.frmGastenboek.submit();	
		}
		else
		{
			alert ("De volgende verplichte velden zijn niet ingevuld:\n\n" + sError);
			bReturn = false;
		}
		return bReturn;
	}