When you say 'package', do you mean like the java.io package kind?
Since that would make absolutly no sense, I will assume that its a jar file.
Now I don't remember exactly how it's done in an applet, I recall getDocumentBase()/getCodeBase() being used somewhere, but in an application instead of this:
Toolkit tk = Toolkit.getDefaultToolkit();
Image image = tk.getImage("image.jpg");
It would be this:
Toolkit tk = Toolkit.getDefaultToolkit();
Image image = tk.getImage(this.getClass().getClassLoader().getResource("image.jpg"));
So I'm sure it's something simliar along those lines, only using the applets getImage method.