[Javascript] readonly in IE7

[John Pillion]

k, I have another question.  I'm trying to mark a text box as readonly 
(from a 'yes/no' radio pair, where disabledValue is the value from the 
radio button - this part works fine). Below is the portion of code, 
which will not work in IE7 (possibly all versions of IE?).

   
    var txtBox = document.forms["bldForm"].elements["bldName"];

    if (disabledValue.toLowerCase() == "y"){
        txtBox.setAttribute('readonly','readonly');
    }else{
        txtBox.removeAttribute('readonly');
    }



I saw elsewhere that the following sometimes is more reliable for IE to 
do the following:

    txtBox.setAttribute('readonly','');
    txtBox.readonly = 'readonly';

this does not work either though, nor does

    txtBox.readonly = 'readonly';