Go to the Java3d download site. If you have Windows, choose the installer named java3d-1_5_1-windows-i586.exe. Download the file. Click on the downloaded file and then follow the instructions.
This page with the instructions will stay open in another window to guide you, as you proceed with the installation.Then go back to Astral Visuals to see the 3D-visuals. You may have to restart the computer to get Java3D to work.
If it still don't work, you will find help in the Java3D-guide .