>> I'm struggling to figure out how to get it on my 32-bit Ubuntu
>> virtual machine. I
>> can't seem to find the correct jdk directory to install java3D into.

  I had same problem on Ubuntu. Installing the package doesn't copy the libraries to your JRE 
distribution for some stupid reason. Do something like:

sudo apt-get install libjava3d-java libvecmath-java
sudo cp /usr/share/java/j3d*.jar  /usr/lib/jvm/java-6-openjdk/jre/lib/ext
sudo cp /usr/share/java/vecmath*.jar  /usr/lib/jvm/java-6-openjdk/jre/lib/ext

(or java-6-sun if you're using that JRE instead)

You'll normally need to restart your IDE to get it to notice the Java 3D libraries (at least I have to with