disable textbox using jquery?

Not really necessary, but a small improvement to o.k.w.'s code that would make the function call faster (since you're moving the conditional outside the function call).

$("#radiobutt input[type=radio]").each(function(i) {
    if (i == 2) { //3rd radiobutton
        $(this).click(function () {
            $("#textbox1").attr("disabled", "disabled");
            $("#checkbox1").attr("disabled", "disabled");
        });
    } else {
        $(this).click(function () {
            $("#textbox1").removeAttr("disabled");
            $("#checkbox1").removeAttr("disabled");
        });
    }
});

HTML

<span id="radiobutt">
  <input type="radio" name="rad1" value="1" />
  <input type="radio" name="rad1" value="2" />
  <input type="radio" name="rad1" value="3" />
</span>
<div>
  <input type="text" id="textbox1" />
  <input type="checkbox" id="checkbox1" />
</div>

Javascript

  $("#radiobutt input[type=radio]").each(function(i){
    $(this).click(function () {
        if(i==2) { //3rd radiobutton
            $("#textbox1").attr("disabled", "disabled"); 
            $("#checkbox1").attr("disabled", "disabled"); 
        }
        else {
            $("#textbox1").removeAttr("disabled"); 
            $("#checkbox1").removeAttr("disabled"); 
        }
      });

  });