[CS3] Can't figure out Enter key in AS 2

[gparis]

input textfield with instance name 'username'

username.text = "";

var myListener:Object = new Object();
myListener.onKeyDown = function () {
    if (username.text.length > 0 && Key.isDown(Key.ENTER)) {
        nextFrame();
    } else {
        trace("empty");
     }
}

Key.addListener(myListener); 

gparis