In JDK1.1 the button class belongs to the component heirarchy. It was not a container to contain other components. In jdk1.2 (otherwise JAVA tm 2) there is an entirely new heirarcy of JObjects. Here we have JButton class, and in one of the constructors of that JButton class you can pass the Icon Object which extends from Image. So this way you have the image on the button.
If you are using JDK1.1 check out the Swing plugin for JDK1.1