I don't know much about Oracle, but many people have asked about Ruby's support for Oracle. One of my clients is also attempting a project with Rails and Oracle. Here are some useful resources I've found:

Starting with Ruby and Oracle : A pretty comprehensive and up to date tutorial about using Oracle with Ruby. The tutorial is written from a Windows perspective.

Ruby/OCI8 (Oracle Call Interface) : A library that provides an interface between Ruby and Oracle 8.

Ruby Oracle 7 library : An alternative for Oracle 7 users.

Ruby and Oracle : A basic tutorial to setting up Ruby and Ruby's Oracle bindings on a Hewlett Packard UNIX based machine.

Rails and Oracle from the official Rails wiki : A whole ton of (older) information about Rails and Oracle integration.

Ruby Oracle DBI ActiveRecord in 7 steps : An up to date tutorial on how to get ActiveRecord running with an Oracle database in 7 easy(ish) steps.