If you want to become a DBA and your company asks you to become one in 30 days, it is a good chance to get an entry into this field. Since you are an Oracle Programmer it will help to a large extent but I would still suggest to propose your company for some formal training. Be thorough with Oracle Architecture and that is your strength. Everything can be related to how well you understood that part. Secondly regards to Manuals and webistes there are 100's..
Go to technet.oracle.com and read as much docs as you can.
Oraclenotes.com, lazydba.com, ora.org, metalink.. so many..
As you go along you will know more and more..
Thx.