More Oracle info here. Didn't find how to enable SSL in the whitepaper, though. But it's a start for you.
Update: apparently, you have to be the DBA to enable SSL in the session, and it's done through the "Oracle Net Manager". More info in the "Oracle Database Advanced Security Administrator's Guide" ^(*), in your copy of the Oracle docs. Hope this helps you get started.
^(*) c. page 64 (2-2) in the "10g" version of the manual, YMMV...