I'm currently a student at New York University studying Computer Science. I've done a fair bit of Java programming. I only wish Apple would bring back support for the JavaBridge so I could use it for my Cocoa work as well.
I've released some open source code based on MattGemmell's original code. I haven't set up a website yet so it's currently hosted on his page: http://iratescotsman.com/products/source/. Look for the ImagePopUpButton example.
I can be reached at ericwang at earthlink dot net.