<input id='r1' type='radio' class='rg' name="asdf"/>
<input id='r2' type='radio' class='rg' name="asdf"/>
<input id='r3' type='radio' class='rg' name="asdf"/>
<input id='r4' type='radio' class='rg' name="asdf"/><br/>
<input type='text' id='r1edit'/>
jquery part
$(".rg").change(function () {
if ($("#r1").attr("checked")) {
$('#r1edit:input').removeAttr('disabled');
}
else {
$('#r1edit:input').attr('disabled', 'disabled');
}
});
here is the DEMO