<html>
<head>
<script language="javascript">
function prueba()
{
alert (eval("document.formulario.boton.value"));
}
</script>
</head>
<body>
<form name="formulario">
<input name="boton" type="radio" value="" onClick="form.boton.value='test1'" checked>boton 1
<br>
<input name="boton" type="radio" value="" onClick="form.boton.value='test2'">boton 2
<br>
<input name="submit" value="Prueba" type="button" onClick="prueba()">
</form>
</body>
</html>