The steam train departures from Trieste aren't scheduled. It's a day tour which takes place two or three times every year: I checked the Museo Ferroviario site (italian only) and there's no mention of next tour. The train trip itself takes about 2-3 hours, including a stop at the border. The links provided by Linda refer to a similar service but from Gorizia to Bled (I guess it's about the same time).

The best way to travel across Slovenia and mainland Croatia is of course by car, but there's an extensive bus service to even the tiniest of villages. I don't know if such schedules are available on the web, as they are operated by local companies, anyway tourist offices should be able to help. I know there are guided tours departing from main cities and tourist resorts, but I doubt they are available off tourist season.

Bye, Paolo Trieste, Italy