is it very important to have that exam and study it? or only the book?
The book should help you learn your way through the technology, and develop key exam skills. A good book will have plenty of
test questions in it too, so you can practise and hone your technique along the way. You won't need any full exams until your knowledge is solid and your results on the test questions are good too.
A mock exam (online, on paper or as part of a software package) will help you review all that you've learnt and give you a chance to test how well you perform answering 63 or so questions in one go. You'll probably want to try at least two mock exams before going for the real thing.
I dont even know where I should get the voucher... is there a specific site with those?..
You're
SCJP certified right? Then you know what you did for that, so repeat the basic procedure once again
Charles Lyons (SCJP 1.4, April 2003; SCJP 5, Dec 2006; SCWCD 1.4b, April 2004)
Author of OCEJWCD Study Companion for Oracle Exam 1Z0-899 (ISBN 0955160340 / Amazon Amazon UK )