Hov, der var lige et par fejl. Sådan her:
<script type="text/javascript">
var oShowText=null;
function showText(o){
o=document.getElementById(o);
if(oShowText)oShowText.style.display="none";
o.style.display="block";
oShowText=o;
}
</script>
<a href="java script:void(0)" onclick="showText('txt1')">Tekst 1</a>
<a href="java script:void(0)" onclick="showText('txt2')">Tekst 2</a>
<a href="java script:void(0)" onclick="showText('txt3')">Tekst 3</a>
<div id="txt1" style="display:none">
Tekst 1 her<br>
Bla bla bla
</div>
<div id="txt2" style="display:none">
Tekst 2 her<br>
<a href="
http://google.com">Google.com</a></div>
<div id="txt3" style="display:none">
Tekst 3 her<br>
<img src="
http://www.google.dk/logos/olympics08_rings.gif"></div>