Mira a ver esto:
Código PHP:
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<script type="text/javascript">
function mostra(obj)
{
var rad1 = document.getElementById("r1");
var rad2 = document.getElementById("r2");
if(obj.id == rad1.id)
{
document.getElementById('radio1').style.display="block";
document.getElementById('radio2').style.display="none";
}
if(obj.id == rad2.id)
{
document.getElementById('radio2').style.display="block";
document.getElementById('radio1').style.display="none";
}
}
</script>
</head>
<body>
<input id="r1" name="" type="radio" value="" onclick="mostra(this)"/>
<span id="radio1" style="display:none">
<input name="" type="checkbox" value="" />
<input name="" type="checkbox" value="" />
<input name="" type="checkbox" value="" />
<input name="" type="checkbox" value="" />
<input name="" type="checkbox" value="" />
</span><br>
<input id="r2" name="" type="radio" value="" onclick="mostra(this)"/>
<span id="radio2" style="display:none">
<input name="" type="checkbox" value="" />
<input name="" type="checkbox" value="" />
<input name="" type="checkbox" value="" />
<input name="" type="checkbox" value="" />
<input name="" type="checkbox" value="" />
<input name="" type="checkbox" value="" />
</span>
</body>
</html>