Eurail and rental cars

Realize what "Eurail" is. It does not operate the trains in Europe, rather, it's a ticketing agency owned by a consortium of various European national rail companies. Eurail's sole reason for existing is to sell overpriced rail passes to non-European citizens. If such a package existed, it would probably originate from a third-party travel agent, and would almost certainly represent a "mark-up of a mark-up". Any savings offered to you would come in the form of someone else doing your homework, not a monetary discount for you. There are some "auto trains" in Europe, particularly on long-haul vacation routes between northern and southern Europe, but I don't think that's what you had in mind. If you want to save money on rail tickets, investigate advanced purchase discounts directly from the national rail companies (ie, Deutsche Bahn for Germany, SNCF for France, etc.).

Carissa, are you referring to the "Rail & Drive Pass"? If you check the "Rail Passes" tab above, you'll find all the info. Personally, if it was my trip, I would do a really quick review of it, then start searching for individual rental agencies (such as autoeurope.com)and all the actual train sites involved, comparing the costs of purchasing train tickets in just a few days vs. buying them 3 months early.