function popup(page,width,height,nom)
{
 if ( width == 0 )
 {
  var windowWidth = screen.width/2;
 }
 else
 {
  var windowWidth = width;
 }
 if ( height == 0 )
 {
  var windowHeight = screen.height/2;
 }
 else
 {
  var windowHeight = height;
 }
 var windowLeft = (screen.width-windowWidth)/2;
 var windowTop  = (screen.height-windowHeight)/2;
 w = window.open(page,nom,'menubar=yes,status=yes,resizable=yes,scrollbars=yes,fullscreen=no,width='+windowWidth+',height='+windowHeight+',top='+windowTop+',left='+windowLeft+' ');
}