function Poker()
{ 
  if (!document.getElementById) return;
  var largeur = document.all?document.body.offsetWidth:window.innerWidth;
  var hauteur = document.all?document.body.offsetHeight:window.innerHeight;
  document.getElementById('poker').style.left = (largeur-250)/2;
  document.getElementById('poker').style.top = (hauteur-250)/2;
  document.getElementById('poker').style.visibility = 'visible'; 
}