Hi, 
Here is the solution to ur problem.It works both in IE and Netscape.
<script language  = "javascript">
function Test()
{
	document.radio_form.options[0].checked = true;
}
</script>



<form name = "radio_form">
	<input type  = "radio" name = "options" id = "1">a
	<input type  = "radio" name = "options" id = "2">b
	<input type  = "radio" name = "options" id = "3">c
	<input type = "button" onClick = "Test();">
</form>

Cheers
Madhan.