Gemini,
I wonder if I might be missing something - you mentioned "where I found classes12.jar"...
I know that previous versions of the Oracle JDBC driver were in a file named "classes12.zip" (and as far as I can remember, the ZIP went in the classpath, and worked like a JAR - been a while, so that sounds iffy now). And in the later version that I am familiar with, it is in ojdbc14.jar... seems reasonable that in the middle at some point it may have been named classes12.jar.
... so I wonder if the classes12.jar you already found is the one you need. But then, you've mentioned it, which makes me think this might be something you already have in your classpath?
Or else, like I said, I'm missing something...
One last thing, that might help tip someone off to the real problem: do you have "oracle.jdbc.driver.OraclePreparedStatement" explicitly in your program? Or is that coming from your program referencing "PreparedStatement", and the specific reference to OraclePreparedStatement is burried in their code? If you're not sure, you can inspect the stack trace for the NoClassDefFoundError.
One (more?) last thing: maybe you could just download the JDBC driver from
Oracle's site instead of trying to find it on your system.
Good luck, hope this helps.
-- Jon