Don't be overly intimidated by the client and server technologies sections of the Sun Certified
Java Associate Exam. Basically, you need to have a high level understanding of these technologies. You don't need to know code - that's for the SCWCD and SCBCD exams, not
SCJA.
Know the definitions of things like WSDL and UDDI, and what they're used for - those are the types of questions you'll get. Wikipedia is actually not a bad place to start for definitions of things like JMS and Web Services - they tend to give a high level overview without getting into too much code.
For an example of what the SCJA exam questions might look like, I have some free mock exams that deal with client and server technologies. Those sample SCJA tests will give you a good idea of the types of questions and answers you'll see on the SCJA examination.
Good luck!
-Cameron McKenzie