The following is what I have in my classpath variable (I double checked and the folder is correct):
The 1.5.2 release of the Java 3D API for Windows 2000, Windows XP (x86 or amd64), and Windows Vista runs on JDK version 1.5.0 and higher. To manually install this release, do the following:
Download and unzip j3d-1_5_2-XXX.zip (using Windows Explorer or an unzip tool such as WinZip) to a temporary download folder, for example, c:\Downloads. This will create a j3d-1_5_2-XXX subfolder in your download folder where the downloaded files can be found. The file you need for manual installation is j3d-jre.zip.
Create a folder for the j3d jar files and native libraries, for example, C:\Users\myhome\j3d, and unzip j3d-jre.zip into this folder.
Modify your CLASSPATH environment variable to include the full paths to j3dcore.jar, j3dutils.jar, and vecmath.jar. For example, add the following to your CLASSPATH variable, using the System control panel, Advanced tab, Environment Variables button:
.;C:\Users\myhome\j3d\lib\ext\j3dcore.jar;C:\Users \myhome\j3d\lib\ext\j3dutils.jar;C:\Users\myhome\j 3d\lib\ext\vecmath.jar
Modify your PATH environment variable to contain the full path to the lib\i386 folder (or lib\amd64 for Windows/x64). For example, on 32-bit Windows, add the following to your PATH variable, using the System control panel, Advanced tab, Environment Variables button.
At this point your Java installation should be able to see the j3d class files. Users of IDEs such as NetBeans and Eclipse should consult the IDE's documentation to see how to add jar files and native libraries to their current project.