There are many good blogs explaining about how you can enter the DBA world. Please review the below links
So you want to become a Oracle DBA
Learning to be a Oracle Database Administrator
Introduction Video to Database Administration
Real Interview Experiences for Sql and Pl/sql Developers
CapGemini PL/Sql Telephonic Interview
Wipro Pl/sql Telefonic Interview
TCS Pl/SQL and SQL Interview Questions Sample