Ferry from Bari or Ancona?

This isn't too helpful, but... I took a ferry from Ancona to Split, and it worked out great- arrived in Split early in the morning and caught the fast hydrofoil to Korcula around 4pm. In your case though, I would recommend the Bari route, since it would position you to work your way north with a minimum of backtracking. The Ancona-Split ferries sail much more often in the off season, but in June I expect Bari-Dubrovnik has frequent sailings as well. My experience is limited to Split and points south... perhaps you could rent a car in Split, drive to Plitvice and perhaps Rovinj? Taking a rental to Slovenia would entail a hefty drop-off fee, but it could still be worth it. Maybe drive to Zagreb or Rijeka and take a bus or train into Slovenia? Good luck-- you might want to post in a TripAdvisor forum or Lonely Planet's Thorn Tree forum for advice on these nitty-gritty details.

Thanks for your input. It seems that it is quite difficult to get to Plitvice without a car.

It might be a better use of your time to fly. Croatia Airlines flies direct from Rome to Split and Dubrovnik (not every day). Otherwise, it's a really long trip to go by land and sea. A suggested itinerary: From Rome, fly to Dubrovnik, use the ferries to visit Korcula and Split, then rent a car for Bosnian destinations and Plitvice. Plitvice is well worth the effort to get there--I've never seen anything else like it! You can drop the car in Zagreb and take the train to Ljubljana (2.5 hrs.) to avoid the hefty drop off fee for dropping a rental in a different country.

Thanks Angela. Does anyone know if there is a place to pick up a rent car at the airport in either Split and/or Zagreb? It is usually easier to find and get to an airport than some address in a city.