score:4
On the map page of the STIB that you mention, you just have to click on "Consultez le plan dynamique" to open the dynamic map. Trains are the dash white and blue lines. Stations have a logo with a white train on a blue background.
In practice you don't have to bother about this. Whenever the train is an option, the STIB journey planner will show it and provide the details.
You should also note that at the time being, train plays a minor role for legs within Brussels.
You can also have a look at the network map if the Belgian Railways (SNCB/NMBS):
http://www.belgianrail.be/fr/service-clientele/outils-voyage/carte-reseau.aspx
The SNCB also provides pdf timetables by line:
http://mobility-brochures.b-rail.be/en/timetable-brochures
Have a look at the following lines: 25, 26, 28, 36, 50, 60, 94, 124 and 161