Thanks for the help!

I had real trouble trying to work out exactly what Oracle components I needed in order to get DBD::Oracle installed. However, after a few dozen Googles I eventually came across:

http://cpanratings.perl.org/dist/DBD-Oracle

From there I discovered that what I had to do after installing the Oracle client was grab this file from Disk2 of the installation media:

stage/Components/oracle.rdbms.oci/9.2.0.4.0/1/DataFiles/public.1.1.jar

Then a "mkdir public" in $ORACLE_HOME/rdbms, cd into public. cp the jar file into public and jar xvf it.

After that, and setting ORACLE_HOME, ORACLE_SID and ORACLE_USERID correctly as you suggested, lo and behold DBD::Oracle fianlly installed :-)