var POPUP=0;

function OuvrirPopup(page)
{ 
if(POPUP) 
{ 
if(!POPUP.closed) POPUP.close(); 
} 
  largeur = 450;
  hauteur = 450;
  ttop=(screen.height-hauteur)/2;
  tleft=(screen.width-largeur)/2;
  POPUP = window.open(page,"affiche","top="+ttop+",left="+tleft+",width="+largeur+",height="+hauteur+",menubar=no,scrollbars=yes,statusbar=no"); 
}