Hi Sureshgane,
I used Jason couchman's book 'Oracle 8 DBA Certification
Exam guide' and STS.
Now a dyas, Exam Cram is available for each paper
which is purely Exam Oriented so you will find these
books are very helpful to exam point of view.

You can also visit [url]http://www.education.oracle.com[/url] for
more info on certification and student guide.

HTH,