var viewportwidth;
var viewportheight;
var scrollTop; 
 // the more standards compliant browsers (mozilla/netscape/opera/IE7) use window.innerWidth and window.innerHeight
function getWidths(){ 
 if (typeof window.innerWidth != 'undefined')
 {
      viewportwidth = window.innerWidth,
      viewportheight = window.innerHeight
 }
 
// IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)

 else if (typeof document.documentElement != 'undefined'
     && typeof document.documentElement.clientWidth !=
     'undefined' && document.documentElement.clientWidth != 0)
 {
       viewportwidth = document.documentElement.clientWidth,
       viewportheight = document.documentElement.clientHeight
 }
 
 // older versions of IE
 
 else
 {
       viewportwidth = document.getElementsByTagName('body')[0].clientWidth,
       viewportheight = document.getElementsByTagName('body')[0].clientHeight
 }


  scrollTop = (document.compatMode != 'CSS1Compat') ? document.body.scrollTop : document.documentElement.scrollTop;


}

   function getTopPos(src){ 
     getWidths();
     return scrollTop+Math.round(viewportheight / 2)-(src.offsetHeight/2)+'px';
   }
   
   function getLeftPos(src){
     getWidths();
     return Math.round(viewportwidth / 2)-(src.offsetWidth/2)+'px';
   }