Hola
disco
Prueba este ejemplo:
Código PHP:
<html>
<head>
<script type="text/javascript">
function activar(obj) {
frm = document.forms[0];
for (i=0; ele = frm.getElementsByTagName('select')[i]; i++)
ele.style.display = (ele==frm[obj]) ? 'block' : 'none';
}
</script>
</head>
<body>
<form>
<input type="radio" name="rad" onclick="activar('pc')" checked="checked" />
<input type="radio" name="rad" onclick="activar('disco')" />
<select name="pc" style="display:block">
<option>pc 1</option>
<option>pc 2</option>
</select>
<select name="disco" style="display:none">
<option>disco 1</option>
<option>disco 2</option>
</select>
</form>
</body>
</html>
Saludos,
