This takes a while to download all of the classes, so be patient -- put your mouse over the applet and look at the bottom of the browser for status.
Getting Java: If this isn't working in Microsoft's Internet Explorer, it's because by default it uses an old, buggy Java implementation. I hate to make you do this, but you may have to download and install Sun's Java Runtime Environment Plugin (J2SE JRE) at http://www.java.com.
Using the Applet: Equations in text boxes are plotted as a function of x. Any free parameters become sliders, which update the graph in real time. Drag on an empty area to move the grph. Drag along the axes to zoom.
Sorry, but right now this is really SLOW. I'm working on it.
The code is liscenced under GPL. It's not complete or presentable yet. You can browse the java directory including source at /java. Archive of the entire directory is java.tar.bz2 (10 MB)