I never been certified as Oracle DBA.
And please don't cry "i'm certified Oracle DBA" on an each coner.
This is'n pletty good practice in each situation.

About ur computer skills:
dba have (not must) to know:
-- hadrware (common system architecture, differense between for example
scsii adb ide ..., types of raids ..., type of buses ... what difference between SMP an MPP...)
-- network architecture (a lot of topics ...)
-- os (filesystems, process managment, user accounts, enviroment,
shell scripting, memory structure, kernel parameters ...+ ...)
-- no less then one programing language (except sql/plsql)
-- OPTION web application servers (no less then "in common")
and HOW IT CAN WOKS TOGETHER and with DB.