I didn't really prepared myself. I have 4 years experience in Java programming. But I think there are a few good books for SCJD. Look at Javaranch.com, there is a list with books for exam.
I started programming with the server IO part. Try writing test cases for this part. Then I implemeneted the networking part and after that changed to the GUI.
I tried to keep things simple. - No table sorting (try to use JDK 1.6, but failed exam - got a free resubmission) - No AND/OR search options in GUI, just 2 textfields - Hardcoded Strings for dialogs and so on - syncronized CRUD(create,read, update, delete) methods - yes I know only one thread could write to file, but I mentioned it in choices.txt
For locking I made a class that represents the lock of one record. In my Data class I have a Hashtable<Long, RecordLock> that holds the objects. You must think about which methods have to be syncronized !!! (so that never ever 2 threads could hold the lock on the same record)