There're big problems around the supporting network of servers (an university is hosting us, so we cannot do too much for bringing network to top shape).

I have installed the one in 3-D. Today, I tried many times to download the other one but the server didn't seem to work.

Hm, I don't have any experience with nuvi.
Let's try to solve step by step: what exe file have you installed?
This one: http://openmaps.eu/rdl.php?id=HR-3D-exe
or this one: http://openmaps.eu/rdl.php?id=HR-2D-exe ?

I have a Garmin nuvi 295W. I have downloaded the maps for Croatia, I have installed them with MapSource. On the GPS, in Map info, I see the initial CN North America... [1]US & Canada and also OpenMaps [1]Zagreb 3D, North Central Croatia... but I can't see the maps of Croatia, whether the OpenMaps is checked or not.
If only the OpenMaps is checked (I uncheck North Amarica), i get a "no map data available" if I try to type an address.
What can I do ? Thank you.