I just finished my part II and III. Although I haven't gotten my grade yet.
Aside from understanding
J2EE and how to apply it, you really need to know UML very well. The hardest part for me was that I was not familar with the UML tool I was using - and so it was more work than it should have been. In hindsight it would have been well worth it to spend a couple of weeks with the tool before working on the exam.
I was talking to someone on e-groups who was considering using Visio to do the diagrams. Let me tell you, it would be a slow torturous process. Best thing I can tell you is to start with a good UML tool, learn to express yourself using it, and then do your best.
dan'l