It is certainly possible to travel by train from elsewhere in Europe to Croatia. The main destinations you can reach by rail are Zagreb, Pula, Rijeka and Split. In the case of the latter, however, you'll definitely have to travel via Zagreb. If you're travelling from northeast Italy - Venice and Trieste - this can add on quite a few hours to your journey, in which case it is better to travel by bus.

A great website to research train travel in Europe is the Die Bahn website. You can search for timetables for practically any journey in Europe, including journeys internal to Croatia.

Useful Train Websites
Check out the following websites for timetable details:

Croatian Railways
Die Bahn

The RailEurope booking engine below might help you get information about your initial journey from, say, the UK to Germany or Austria. Booking to Croatian stations isn't yet available!