ho provato ma non funziona lo stesso... selezionando più volte pippo pluto pippo pluto ecc. la table diventa sempre più grande...

forse ho sbagliato qualche altra cosa?

in ogni caso ti ringrazio, ciao!

<html>
<head>
<title></title>
<script LANGUAGE="JavaScript">
function cambioOsi() {
osiOgg = document.getElementById('osi');
osiValue = osiOgg.options[osiOgg.selectedIndex].value;
if(osiValue=="1" ) {
document.getElementById('group3').style.display='i nline';
document.getElementById('group8').style.display='i nline';
}
else {
document.getElementById('group3').style.display='n one';
document.getElementById('group8').style.display='n one';
}
}
</SCRIPT>
</head>
<body BGCOLOR="#ffffff" >
<div ALIGN="center">
<form NAME="F_1" ID="F_1">
<table BORDER="1" CLASS="tab" WIDTH="300">
<tr>
<td>
<table CELLSPACING="0" CELLPADDING="2" DATAPAGESIZE="2" BORDER="0">
<tr>
<th ID="mandatory" NOWRAP WIDTH="100" align="right">Tipologia</th>
<td>
<select NAME="osi" ID="osi" onchange="cambioOsi();" >
<option VALUE="0" SELECTED></option>
<option VALUE="1">pippo</option>
<option VALUE="2">pluto</option>
</select>
</td>
<td NOWRAP ID="class1" STYLE="display:none">Anno origine</td>
<td ALIGN="left" ID="class2" STYLE="display:none"><input TYPE="text" SIZE="6"></td>
</tr>
</table>
<table border="1">
<tr ID="group3" STYLE="display:none" >
<th ALIGN="right" ID="mandatory" WIDTH="100">Tipo UA</th>
<td COLSPAN=3>
<select NAME="tipoAttributo" ID="tipoAttributo" >
<option VALUE="0" SELECTED></option>
<option VALUE="1">Popolazione</option>
<option VALUE="2">flusso di eventi</option>
</select>
</td>
</tr>
<tr ID="group8" STYLE="display:none">
<th ALIGN="right" WIDTH="100">Tipo osservazione</th>
<td COLSPAN="3" NOWRAP>VA OSSERVATA INDIVIDUALMENTE</td>
</tr>
</table>
</td>
</tr>
</table>
</form>
</div>
</body>
</html>