If you fancy using BlueJ on Mac OS X, head over to bluej.org and grab the stable version for Mac OS X. Once downloaded you will have the BlueJ folder, just put this where you keep your other apps. This is a stock BlueJ install so you will need to add the OU components.

Instructions

1. Right click, or control click if you have a single button mouse on the BlueJ icon. Select the option “Show Package Contents” this will open a window with a folder named “Contents”.

2. Navigate to the userlib folder Contents > Resources > Java > userlib.

3. Pop in the Course software CD, at the root of the CD is a folder named “libraryfiles” go inside here and copy the files bsh-2.0b4.jar and ou.jar to the userlib folder opened in the last step.

4. Next navigate to the folder Contents > Resources > Java > extensions.

5. From the root of the course CD copy the jars “eaextension.jar” and “ouwextension.jar”.

6. In the Finder navigate to the folder named Library in the root of your hard drive and scroll down to the folder Java, copy the same two jars bsh-2.0b4.jar and ou.jar
to the folder named Extensions.

Quick listing:
Inside BlueJ application bundle:
Resources > Java > extensions should contain the following:
eaextension.jar
ouwextension.jar

Inside BlueJ application bundle:
Resources > Java > userlib should contain
bsh-2.0b4.jar
ou.jar

In the Library Folder in the Hard Drive and not in your home folder.
/Library/Java/Extensions should contain the following:
bsh-2.0b4.jar
ou.jar

Thats it done. Now your good to go!

Note: I have seen another site that says to put bsh-2.0b4.jar and ou.jar in /System/Library/Frameworks/JavaVM.framework/Versions/1.5.0/Home/lib/ext/ this location is the actual Java system and should not really be touched. The Location /Library/Java/Extensions is the official location for additional jars and classes specified by Apple, all extensions are loaded when the JavaVM is started up. Another advantage of this approach is that if Apple updates the Java installation which is common this location is static and will just work with future versions.

If you want some more info, or find this useful leave me a comment.