Ive been a part time dba for 4 years with mixed experience of using many pre9 databases on several platforms. Reading this book has taught me about the lesser used features of 9i, as well as building upon my knowledge as a whole - but there seem to be plenty of errors in the book, so digest with caution.
As suggested by Oracle, you will also need experience to pass the exam, as the book's examples are somewhat simplified and lacking in the type of "choose 3 correct answers out of the 6" questions which the actual exam seems full off. This means that unless you know your stuff, getting one of the 'n' answer questions wrong, means that you lose the whole mark. And with a passmark of 73% (at the time of writing) this can be make a difference.
Take your time with this book and investigating all the suggested views and making sure that you perform the exercises, (reading around the edges where necessary ) and this should help you pass.
Over all, a good book (and highly recommended despite my warnings), but is by no means the only thing you will need to pass the exams. Do check out the errata section of the osbourne site though: