Prova così:
codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Form</title>
<style type="text/css">
<!--
#theFormDiv {
 	display:none;
 	position:absolute;
 	top:4em;
 	left:4em;
 	background-color:#EEE;
 	border:1px solid #000;
 	padding:1em;
 	margin:3em;
 	width:20em;
}
.nocss {
  	display:none;
}
</style>
<script type="text/javascript">
function showForm(nome,pz) {
  	oDiv = document.getElementById('theFormDiv');
  	oDiv.style.display='block';
document.getElementById('prezzo').value=pz;
document.getElementById('nome').value=nome;
  	return false;
	}

	function hideForm() {
  	oDiv = document.getElementById('theFormDiv');
  	oDiv.style.display='none';
document.getElementById('prezzo').value='';
document.getElementById('nome').value='';
  	return false;
	}

</script>
</head>

<body>
<table width="900" border="1" cellspacing="0" cellpadding="0">
  <tr>
    <td width="89" class="tab"><div align="center">Nome</div></td>
    <td width="89" class="tab"><div align="center">Prezzo</div></td>
    <td width="93" class="tab"><div align="center">Azioni</div></td>
  </tr>
  <tr>
    <td width="89" class="tab"><div align="center">Zlatan</div></td>
    <td width="89" class="tab"><div align="center">10$</div></td>
    <td width="93" class="tab"><div align="center">
    ','<? echo $row['prezzo']; ?>');">Modifica
    </div></td>
  </tr>
</table>
<div id="theFormDiv">
  <form method="post" id="frm" action="index.php">
    <fieldset>
      <legend>Modifica Upgrade</legend>
      <table>
        <tr><td><label id="label-first">Nome</td><td><input name="nome" type="text" id="nome"></td></tr>
         <tr><td><label id="label-email">Prezzo</td><td><input name="prezzo" type="text" id="prezzo"></td></tr>
         <tr><td><input type="submit" id="bSubmit" name="bSubmit" value="Modifica" onclick="hideForm();"></td>
         <td><input type="button" id="bCancel" name="bCancel" value="Annulla" onclick="hideForm();"></td></tr>
       </table>
     </fieldset>
  </form>
</div>
</body>
</html>