try this:
and change according to your requirement.
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Untitled Document</title>
<script type="text/javascript">
function changeValue(x)
{
var divEls = document.getElementsByTagName("div");
var i = 0;
for(i=0;i<divEls.length;i++)
{
divID=divEls[i].id;
//alert(divID);
//alert(x);
if(divID == x)
document.getElementById(divID).style.visibility = "visible";
else
document.getElementById(divID).style.visibility = "hidden";
}
}
</script>
</head>
<body>
<select name="htmlcombo" id="htmlcombo" onChange="changeValue(this.value);">
<option value="0">Select</option>
<option value="1">Display Text1</option>
<option value="2">Display Text2</option>
<option value="3">Display Text3</option>
</select>
<div id="1" style="visibility:hidden" >hello1</div>
<div id="2" style="visibility:hidden">hello2</div>
<div id="3" style="visibility:hidden">hello3</div>
</body>
</html>