// Fensterhoehe liefern
function get_window_height(){
if (document.all){
return document.body.clientHeight;
}
else if (document.layers){
return window.innerHeight;
}
}

// Fensterbreite liefern
function get_window_width()
{
if (document.all){
return document.body.clientWidth;
}
else if (document.layers){
return window.innerWidth;
}
}

function bewege(){
window.moveTo ( (screen.width/2)-(get_window_width()/2), 
(screen.height/2)-(get_window_height()/2) );
}