function openvenster(url,popup_width,popup_height,scrollbars) {
    var undefined;
    if (popup_width == undefined) popup_width=800;
    if (popup_height == undefined) popup_height=600;
    if (scrollbars == undefined) scrollbars='no';
    left_pos = (screen.availWidth/2) - (popup_width / 2);
    top_pos = (screen.availHeight/2) - (popup_height / 2);
    mywin = window.open(url,'popup','height=' + popup_height + ',left=' + left_pos + ',top=' +top_pos + ',width=' + popup_width + ',scrollbars=' + scrollbars);
    mywin.focus();
}

function wallpaper(wpid) {
	openvenster('wallpaper.php?wpid='+ wpid,1024,768,true);
}