Código:
<script>
var chk = 0
function hola() {
for (i=1;i<3;i++) {
if (document.getElementById('r'+i).checked==true) {
chk = 1;
}
}
if (chk==1) {alert("Has checkeado")}
else {alert("no has checkeado")}
}
</script>
<body>
<form name="form1">
<label>
<input name="RadioGroup1" type="radio" id="r1" value="radiobutton">
RadioGroup1</label>
<input name="RadioGroup1" id="r2" type="radio" value="radiobutton" >
RadioGroup2
<label>
<input type="button" name="Submit" value="Enviar" onClick="hola()">
</label>
</form>
</body>
</html>
De nada, todo un placer ayudarte,
saludos