function bildwechsel(bild) {

var bildquelle;
   switch(bild)
   {
      case 1: bildquelle="img/text_leer.gif"; break;
      case 2: bildquelle="img/text_popup.gif"; break;
      case 3: bildquelle="img/text_flashflash.gif"; break;
      case 4: bildquelle="img/text_videomail.gif"; break;
      case 5: bildquelle="img/text_rectangle.gif"; break;
      case 6: bildquelle="img/text_skyscraper.gif"; break;
      case 7: bildquelle="img/text_videobanner.gif"; break;
  }
  window.document.erklaerung.src = bildquelle;
}

system=navigator.appVersion

        gosystem= system.indexOf("Macintosh")
        //document.write("<br>")

        if (gosystem =="-1")
        {
        gosystem="Windows"
        //document.write(gosystem)
        }
        else
        {
        gosystem="Macintosh"
        //document.write(gosystem)
        }

function fenster(url,name,w,h) {

if ((navigator.appName=="Netscape") && (gosystem=="Windows"))
{
h3=h-8
w3=w-2
Breite=screen.width
Hoehe=screen.height

hzwei=h*0.5
wzwei=w*0.5

oben=Hoehe*0.5-hzwei
links=Breite*0.5-wzwei
                        picWindow=window.open(url,name,"width="+w3+",height="+h3+",top="+oben+",left="+links);
                        picWindow.focus();
}

else if ((navigator.appName=="Netscape") && (gosystem=="Macintosh"))
{
h3=h-4
Breite=screen.width
Hoehe=screen.height

hzwei=h*0.5
wzwei=w*0.5

oben=Hoehe*0.5-hzwei
links=Breite*0.5-wzwei
                        picWindow=window.open(url,name,"width="+w+",height="+h3+",top="+oben+",left="+links);
                        picWindow.focus();
}

else if ((navigator.appName=="Microsoft Internet Explorer") && (gosystem=="Windows"))
{
w2=w
h2=h
Breite=screen.width
Hoehe=screen.height

hzwei=h*0.5
wzwei=w*0.5

oben=Hoehe*0.5-hzwei
links=Breite*0.5-wzwei
                        picWindow=window.open(url,name,"width="+w2+",height="+h2+",top="+oben+",left="+links);
                        picWindow.focus();
}

else if ((navigator.appName=="Microsoft Internet Explorer") && (gosystem=="Macintosh"))
{
w2=w-16
h2=h-16
Breite=screen.width
Hoehe=screen.height

hzwei=h*0.5
wzwei=w*0.5

oben=Hoehe*0.5-hzwei
links=Breite*0.5-wzwei
                        picWindow=window.open(url,name,"width="+w2+",height="+h2+",top="+oben+",left="+links);
                        picWindow.focus();
}

}