First approach: bare metal
require \'java\' require \'rubygems\' require \"c:/ruby/jruby-1.2.0/lib/ojdbc14.jar\" # should be redundant, but tried it anyway
It turns out that my ojdbc14.jar file was corrupt.
Further, the jar file MUST be in the jruby/lib directory. Simply having it on the classpath does not work.