First congrats on your great score in the SCJP.
The SCJD is different from the SCJP, in that there is really no preparation to be done. No mock exams, no books to read, no pre-knowledge you have to have, otherwise you will fail miserably.
No, this exam is an assignment, and in that it is a learning tool in and of itself. You can immediately sign up for the assignment, download it and go. You have an unlimited amount of time to complete the assignment.
You will post lots of questions here, read lots of posts, do searches here, et al.
If you have to have a book, I high suggest the RHE, Roberts, Heller, Ernest book on
Java Certification, it covers SCJP and SCJD. It will let you in on the areas of the assignment, which are RMI, Swing, and a couple of design
patterns like Proxy, Adapter, Factory, MVC, and Facade.
I say go sign up and start coding.
Mark