Hi,
Jason couchman's book 'Oracle 8 DBA certification Exam Guide' is good book for preparation and also STS, Exam Cram
are very helpful as they are exam oriented :)
HTH,
Good Luck
Regards,
Vimal Patel
OCP DBA 7.3, 8, 8i, 9i
Sun Solaris 8 Sys. Admin.
A+