Esempio:
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<script type="text/javascript" language="javascript">
function AbilitaForm(layerform){
if(layerform==1){
document.getElementById('form_1').style.visibility='visible';
}else{
document.getElementById('form_1').style.visibility='hidden';
}
if(layerform==2){
document.getElementById('form_2').style.visibility='visible';
}else{
document.getElementById('form_2').style.visibility='hidden';
}
if(layerform==3){
document.getElementById('form_3').style.visibility='visible';
}else{
document.getElementById('form_3').style.visibility='hidden';
  }
}
</script> 
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Documento senza titolo</title>
</head>

<body>
<table border="0" cellpadding="0" cellspacing="0" width="100%">
    <tr>
        <td width="957" height="21">
            <form name="form1" action="prova.asp" method="get">
                


				<select name="Select_Form" size="1" onChange="AbilitaForm(this.value);">
                    <option value="0" selected>Seleziona</option>
                    <option value="1">Form1</option>
                    <option value="2">Form2</option>
                    <option value="3">Form3</option>
                                </select></p>
            </form>
            <div id="form_1" style="width:282px; height:200px; position:absolute; left:10px; top:90px; z-index:1; visibility:hidden;">
                

Contenuto Form Uno</p>
            </div>
            <div id="form_2" style="width:285px; height:202px; position:absolute; left:10px; top:90px; z-index:1; visibility:hidden;">
                

Contenuto Form Due</p>
            </div>
            <div id="form_3" style="width:284px; height:200px; position:absolute; left:10px; top:90px; z-index:1; visibility:hidden;">
                

Contenuto Form Tre</p>
            </div>
</td>
    </tr>
</table>


</body>
</html>