function Hintergrund(Bild) {
if (Bild == 1) document.getElementById("wrapper2").style.background="url('bilder/bg_1.jpg')";
if (Bild == 2) document.getElementById("wrapper2").style.background="url('bilder/bg_2.jpg')";
if (Bild == 3) document.getElementById("wrapper2").style.background="url('bilder/bg_3.jpg')";
if (Bild == 4) document.getElementById("wrapper2").style.background="url('bilder/bg_4.jpg')";
if (Bild == 5) document.getElementById("wrapper2").style.background="url('bilder/bg_5.jpg')";
if (Bild == 6) document.getElementById("wrapper2").style.background="url('bilder/bg_6.jpg')";
if (Bild == 7) document.getElementById("wrapper2").style.background="url('bilder/bg_7.jpg')";
if (Bild == 8) document.getElementById("wrapper2").style.background="url('bilder/bg_8.jpg')";
if (Bild == 9) document.getElementById("wrapper2").style.background="url('bilder/bg_9.jpg')";
if (Bild == 10) document.getElementById("wrapper2").style.background="url('bilder/bg_10.jpg')";
if (Bild == 11) document.getElementById("wrapper2").style.background="url('bilder/bg_11.jpg')";
if (Bild == 12) document.getElementById("wrapper2").style.background="url('bilder/bg_12.jpg')";
if (Bild == 13) document.getElementById("wrapper2").style.background="url('bilder/bg_13.jpg')";
if (Bild == 14) document.getElementById("wrapper2").style.background="url('bilder/bg_14.jpg')";
if (Bild == 15) document.getElementById("wrapper2").style.background="url('bilder/bg_15.jpg')";
if (Bild == 16) document.getElementById("wrapper2").style.background="url('bilder/bg_16.jpg')";
if (Bild == 17) document.getElementById("wrapper2").style.background="url('bilder/bg_17.jpg')";
}

/*
html
<link rel="stylesheet" type="text/css" href="standard.css" title="standard" />
<link rel="alternate stylesheet" type="text/css" href="slide_1.css" title="slide_1" />
<link rel="alternate stylesheet" type="text/css" href="slide_2.css" title="slide_2" />

Aufruf
<a href="#" onclick="setActiveStyleSheet('slide_16'); return false;"><img src="bilder/slide_16.jpg" /></a>

JS
function setActiveStyleSheet(title) {
  var i, a, main;
  for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
    if(a.getAttribute("rel").indexOf("style") != -1 && a.getAttribute("title")) {
      a.disabled = true;
      if(a.getAttribute("title") == title) a.disabled = false;
    }
  }
}

function getActiveStyleSheet() {
  var i, a;
  for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
    if(a.getAttribute("rel").indexOf("style") != -1 && a.getAttribute("title") && !a.disabled) return a.getAttribute("title");
  }
  return null;
}

function getPreferredStyleSheet() {
  var i, a;
  for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
    if(a.getAttribute("rel").indexOf("style") != -1
       && a.getAttribute("rel").indexOf("alt") == -1
       && a.getAttribute("title")
       ) return a.getAttribute("title");
  }
  return null;
}

function createCookie(name,value,days) {
  if (days) {
    var date = new Date();
    date.setTime(date.getTime()+(days*24*60*60*1000));
    var expires = "; expires="+date.toGMTString();
  }
  else expires = "";
  document.cookie = name+"="+value+expires+"; path=/";
}

function readCookie(name) {
  var nameEQ = name + "=";
  var ca = document.cookie.split(';');
  for(var i=0;i < ca.length;i++) {
    var c = ca[i];
    while (c.charAt(0)==' ') c = c.substring(1,c.length);
    if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
  }
  return null;
}

window.onload = function(e) {
  var cookie = readCookie("style");
  var title = cookie ? cookie : getPreferredStyleSheet();
  setActiveStyleSheet(title);
}

window.onunload = function(e) {
  var title = getActiveStyleSheet();
  createCookie("style", title, 365);
}

var cookie = readCookie("style");
var title = cookie ? cookie : getPreferredStyleSheet();
setActiveStyleSheet(title);
*/