function centerPopUp( url, name, width, height, scrollbars ) { 

if( scrollbars == null ) scrollbars = "0" 

str = ""; 
str += "resizable=1,"; 
str += "scrollbars=0" + scrollbars + ","; 
str += "width=" + width + ","; 
str += "height=" + height + ","; 

if ( window.screen ) { 
var ah = screen.availHeight - 38; 
var aw = screen.availWidth - 160; 

var xc = ( aw - width ) / 2; 
var yc = ( ah - height ) / 2; 

str += ",left=" + xc + ",screenX=" + xc; 
str += ",top=" + yc + ",screenY=" + yc; 
} 
window.open( url, name, str ); 
} 

//<a title="Panorama-Tour Lienz | Osttirol" href="http://www.ausserlechner.net/360_tours/360_pano_lienz_hauptplatz/tour_lienz_pop.htm" onclick="centerPopUp( 'http://www.ausserlechner.net/360_tours/360_pano_lienz_hauptplatz/tour_lienz_pop.htm', 'popup', 726, 540 ); return false;">&gt;&gt; Panorama Tour Lienz starten!</a>