function centerPop(url,popName,popWidth,popHeight) {
	// onClick="return centerPop('url','popupname',600,400);"
    var popWidth;
	var popHeight;
	var screenWidth  = window.screen.width;
    var screenHeight = window.screen.height;
    var placementx   = (screenWidth/2)-((popWidth)/2);
    var placementy   = (screenHeight/2)-((popHeight+50)/2);

    window.open(url,popName,"width="+popWidth+",height="+popHeight+",toolbar=0,location=0,status=0,scrollbars=yes,menubar=0,resizable=0,left="+placementx+",top="+placementy+",screenX="+placementx+",screenY="+placementy+",");
}