var popUpWin=0;
function showHelp(helpFile){
	screen_width = screen.width;
	screen_height = screen.height;
	window_width = 500;
	window_height = 300;
	window_left = (screen_width - window_width) / 2;
	window_top = (screen_height - window_height) / 2;
	if(popUpWin){
		if(!popUpWin.closed) 
			popUpWin.close();
	}
		popUpWin = open(helpFile, 'Help', 'toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=no,copyhistory=yes,width='+window_width+',height='+window_height+',left='+window_left+', top='+window_top+',screenX='+window_left+',screenY='+window_top+'');
}