function openWindow(url, theWidth, theHeight, scrollBars) {
    if (document.all)
        var xMax = screen.width, yMax = screen.height;
	else
        if (document.layers)
			var xMax = window.outerWidth, yMax = window.outerHeight;
		else
			var xMax = 640, yMax=480;
	
	var xOffset = (xMax - theWidth)/2, yOffset = (yMax - theHeight)/2;
	
	if (scrollBars==true)
	  sBar = 'scrollbars=yes';
	else
	  sBar = 'scrollbars=no';
	  
    window.open(url,'viewer','width='+theWidth+',height='+theHeight+',screenX='+xOffset+',screenY='+yOffset+',top='+yOffset+',left='+xOffset+','+sBar+'');
}