DBD::Oracle is just the perl module, but it still requires either a full database installation or an Oracle-client installation. The message possibly stems from the shared object of the perl module not able to find the Oracle client libraries. I know how to show what Oracle.so expects on Linux/Unix, but I have no idea how to show that on Windows.
Did you install the Oracle client where DBD::Oracle expects it? Dit you read the documentation for win64/win32 about the prerequisites?
Enjoy, Have FUN! H.Merijn