JQuery :: Use AjaxSetup To Define A Username And Password That Will Then Be Used By GetJSON?

Is it possible to use ajaxSetup to define a username and password that will then be used by getJSON? I have an enviuronment where I have a web server that I'm passing a URL to for a web service call that returns me JSON. I'm doing the call via the getJSON method, and get back the data I want, except that I'm being prompted to log in and I don't want the users to authenticate. I need to provide a username and password somewhere in the URL (or additional details) and so added an ajaxSetup call right before I call getJSON to set the username and password as follows:

jQuery.ajaxSetup({username: myusername, password: mypassword });
jQuery.getJSON(url, function (jsonObject) {
//do some stuff
}
);

For some reason I'm still getting prompted for the username and password for the URL, even though they're being set. I'm working with IE6, and jQuery 1.3.2.