First, go to Sun's site and read the "Success Guide"
http://suned.sun.com/US/images/certification_archj2ee_07_01.pdf - the really important part is the Objectives.
Then come back here to find out everything you can about what they mean. The objectives are pretty vague, but the folks here seem very willing to share their hard-earned knowledge about what Sun's really looking for.
Good luck,
Burk
SCJP, SCJD, SCEA 5 "Any sufficiently analyzed magic is indistinguishable from science!" Agatha Heterodyne (Girl Genius)