AutoDesk has a bizarre approach to setting up their Java-based MapGuide client. In theory, it should work on most platforms – but they only document it on Internet Explorer on a few platforms, and on Netscape 4.x on Solaris. On top of that, most of their installation instructions require using an extra Java applet to do the installation, or downloading a big shell script for Solaris.
I got it to work under Mozilla Firefox on Linux, and I’m sure it would work like this on Windows or MacOS as well. Here’s how I did it; adapt my approach to your setup.

1. Download the JAR archive (mgjava.jar) from here.
2. Try to figure out where to install it. I did this by visiting the VanMap website, which fails to load since it can’t find the JAR file. I right-clicked on the broken Java applet, which brought up a menu that allowed me to open the Java console. On my Java installation (J2RE 1.4), I got an error message like this:
   
load: class com/autodesk/mgjava/MGMapApplet.class not found.
java.lang.ClassNotFoundException: com.autodesk.mgjava.MGMapApplet.class
at sun.applet.AppletClassLoader.findClass(AppletClassLoader.java:162)
at java.lang.ClassLoader.loadClass(ClassLoader.java:289)
at sun.applet.AppletClassLoader.loadClass(AppletClassLoader.java:123)
at java.lang.ClassLoader.loadClass(ClassLoader.java:235)
at sun.applet.AppletClassLoader.loadCode(AppletClassLoader.java:566)
at sun.applet.AppletPanel.createApplet(AppletPanel.java:617)
at sun.plugin.AppletViewer.createApplet(AppletViewer.java:1863)
at sun.applet.AppletPanel.runLoader(AppletPanel.java:546)
at sun.applet.AppletPanel.run(AppletPanel.java:298)
at java.lang.Thread.run(Thread.java:534)

   and instructions telling me to press “s” to view the system properties. I did that, and found the Java CLASSPATH setting java.class.path = /usr/lib/j2se/1.4/jre/classes. If you can find that classpath setting, you’re good to go.
3. Go to the classpath directory. On my system, the “classes” subdirectory didn’t exist and I had to create it. Unzip the mgjava.jar file to there (yes, JAR files are just zip archives).
4. Restart Firefox. Visit the VanMap website again and see if everything’s working.

This whole procedure is amazingly painful. Debian’s documentation claims that the classpath is something different – they say it’s in /usr/share/java/repository. There are some jar files in /usr/share/java, but there is no repository directory. Installing the jar file there didn’t help at all. It’s also annoying that you have to unzip the jar file – that wasn’t obvious to me at all. Sigh… at least I’ve got it working now.