var iswindowopen = false;
var mw;
function centerWindow(theURL,winName,wSize,hSize)
{
	if (iswindowopen) {
		if (!mw.closed){
		  mw.close();}
        }
	var xMax = screen.width, yMax = screen.height;
	var xOffset = (xMax - wSize)/2, yOffset = (yMax - hSize)/2;
	if (navigator.appname != 'Netscape')	{
	mw = window.open(theURL,winName,'width='+wSize+',height='+hSize+',scrollbars=yes,resizable=no,top='+yOffset+',left='+xOffset+'');
	}else{
	mw = window.open(theURL,winName,'screenX='+wSize+',screenY='+hSize+',scrollbars=yes,resizable=no,top='+yOffset+',left='+xOffset+'');
	}
	mw.focus();
	iswindowopen = true;}