To get the DBA certification you must first take the OCA exam:
1Z0-042 Oracle Database 10g: Administration I
Then you take the final OCP exam:
1Z0-043 Oracle Database 10g: Administration II
Then you must complete a hands-on course to get the certification.
It's all listed here:
http://education.oracle.com/pls/web_pro ... ge_id=47#2
The other exam (1Z0-040) is an upgrade exam for existing Oracle 9i DBA OCPs, so it's not relevant for you.