To be explicit, I am doing a GUI application with a "start" button among others. Once the "start" button is clicked, another gui jumps out and asks for a username and subject. I have done this with a JOptionPane method but wish I could be more expressive with another frame. however this has proved to be difficult.
The easiest thing to do is create a JDialog. It's basically a JFrame that can be modal (when it's open, the other application frames are inaccessable). You can add any component to it that you want, just like a JFrame.
Take a look at the Dialog tutorial on Sun's Swing Tutorial. It will show you how to use the JDialog class.