How would I travel from Paris to Zagreb, Croatia, then from Croatia to Amsterdam by train?

I'm going to be traveling from London to Paris to Croatia then up to Amsterdam. I plan on taking a boat from London to Paris but how would I go about getting from Paris to Croatia then to Amsterdam. Would I need some kind of Eurailpass? I looked at their website and apparently they you have to be traveling in countries that are connected?

Please help! Thanks!

you seem to have answered your own question.

Try www.hznet.hr, thats the Croatian railways. Then click on english (top right), then on the bottom left there's a list for timetables, including international destinations.
You'll have to go to another main station and change trains, because I don't think there are any direct lines. If you got to say, Trietse in Italy, or Vienna in Austria with Eurail, you could always go by bus straight to Zagreb from there.

Try www.autotrans.hr, or www.croatiabus.hr they both have english options.
Good luck!!