<form name="myForm">
<input name="radiobutton" type="radio" value="0" checked onClick="getChoice();" />
Radio1
<input name="radiobutton" type="radio" value="1" onClick="getChoice();" />
Radio2
<input name="Num" type="text" />
</form>
<script language="javascript">
function getChoice() {
if(document.myForm.radiobutton[0].checked) {
document.myForm.Num.value=document.myForm.radiobutton[0].value;
} else if (document.myForm.radiobutton[1].checked) {
document.myForm.Num.value=document.myForm.radiobutton[1].value;
}
}
</script>