If you intend to work with the embeded OC4J, the first tip will be to check if the Tools->Start WebCenter Preconfigured OC4J is working.
You may encounter the following error:
Error# Can not find java executable in /System/Library/Frameworks/JavaVM.framework/Versions/1.5.0/Home/../bin.
This is easy to correct.
Choose Tools->External Tools
Then Edit Start WebCenter Preconfigured OC4J
Remove the dots after "Home"
Repeat the same with the "Stop WebCenter Preconfigured OC4J" tool and you are set for OC4J.
Next time I'll try to show you interaction between Groovy and OC4J ;)