var viewportwidth = 0;
 var viewportheight = 0;
 
function WindowSize(){
 // the more standards compliant browsers (mozilla/netscape/opera/IE7) use window.innerWidth and window.innerHeight
 
 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
 }
 if (viewportwidth < 800)
 viewportwidth = 800
  if (viewportheight < 600)
 viewportheight = 600
 }