First check if you got the latest Java-version .
Then go to Sun's site and follow the instructions below on this page.This page with the instructions will stay open in another window to guide you, as you proceed with the installation on Sun's site.
Press the first "Download"-button, the one below "Download Java 3D API 1.5.0 ". A new window will open.
Press "Accept" and choose Java3D for your platform (probably Windows).
After the download is complete, open the file you have downloaded.
The wizard starts and will guide you. You only have to press "next", until you reach the "done"-button. Press it and you are finished!
Then go back to Astral Visuals to see the 3D-visuals. You may have to restart the computer to get Java3D to work.
If they still don't work, you will find help in the Java3D-guide .
If you use other operating systems than Windows or Solaris go here to find Java3D.