function popup(u,n,b,h)
{
var breite = b;
var hoehe = h;
var y = (screen.height-h)/2;
var x = (screen.width-b)/2;
var name = n;
var url = u;
var parameter ="width=" + breite + ",height=" + hoehe + ",left=" + x + ",top=" + y;

fenster = window.open(url,name,parameter);
fenster.focus();
}