jQuery will automatically parse the JSON string into a JavaScript object for you to use.
Code:
function get_twitter() {
$.getJSON("http://twitter.com/statuses/user_timeline/fredkelly.json?count=1&callback=?", function (data){
// Alert the twitter message only
alert(data[0].text);
// Add it to the page (assumes you have an element id "foo")
document.getElementById("foo").innerHTML = data[0].text;
});
}