$do_toggle = "onClick="javascript:toggle('togglenote');"";

echo form_radio('decision'.$key,'y',FALSE,$do_toggle)."Yes ";

echo form_radio('decision'.$key,'n',FALSE,$do_toggle)."No";

echo form_input($mytext);

// I put a div tag around the form_input above
// but it's not showing in the StackOverflow question...
// but it's there for the toggle to work.

<input type="checkbox" name="decisionY" value="y" /> Yes
<input type="checkbox" name="decisionN" value="N" /> Yes
<input type="text" id="togglenote" name="togglenote" />

$(document).ready(function(){
  $(":checkbox[name^='decision']").change(function(){
     if($(this).is(":checked")){
        $(":checkbox[name[^='decision']").attr("checked", false); //Uncheck the other
        $(this).attr("checked", true);
        $("#togglenote").show();
     }
     if($(":checkbox[name^='decision']:checked").size() == 0){
        $("#togglenote").hide();
     }
  });
});

$("#checkbox1").change(function() {

if ($(this).attr("checked") && $("#checkbox2").attr("checked")) {
   $("checkbox2").removeAttr("checked");
} else if ($(this).attr("checked")) {
   $("#inputfield").show();
} else {
   $("#inputfield").hide();
}
});


$("#checkbox2").change(function() {

if ($(this).attr("checked") && $("#checkbox1").attr("checked")) {
   $("checkbox1").removeAttr("checked");
} else if ($(this).attr("checked")) {
   $("#inputfield").show();
} else {
   $("#inputfield").hide();
}
});