Several resources to choose from:
Exam Cram Oracle 8 DBA Performance Tuning by Ault and Brinson, published by Coriolis. This book is the best, most closely tailored publication for the exam itself.
Oracle Press DBA Exam Certification Guide by Jason Couchman. Not quite as thorough on this subject, but still quite useful.
O'Reilly also has a book
http://www.oreilly.com/catalog/oracle2/

I found this test to be the most difficult and perhaps containing the most demonic questions. It also has the highest pass threshold, around 78%.
It is very important not only to study the books, but to put into practice the teachings on your own database. Study the data dictionary views, learn the various hit ratios completely, learn the memory architecture and create practice problems on the db for yourself.
Finally, take several practice tests before you go in to the real test.