I asked this question yesterday (http://stackoverflow.com/questions/7392321/how-do-you-disable-a-button-inside-of-an-alertdialog) and modified my code accordingly... this mornin
The trick is that you need to use the AlertDialog object retuned by AlertDialog.Builder.show() method. No need to call AlertDialog.Builder.create().
Example:
        AlertDialog dialog = alertbox.show();
        if(monsterint > playerint) {
            Button button = dialog.getButton(AlertDialog.BUTTON_NEUTRAL);
            button.setEnabled(false);
        }