Ok.. I'm trying to get this quake 3 map loaded into irrlicht, but as you can see from the picture below... it doesn't look right at all. The floor has somehow vanished!
Looks to me like a nasty case of the back-face-culling-nitus. Try setting the backface culling material flag to false to see if thats the case.
Also, IIRC, the problem is that the normals are in the wrong direction so if you try to do collision, there might be problems. I'm not entirely sure, though.
Normals aren't used for collision, the winding order is, same for backface culling i believe.
Check your console output, does it say it's failed to load a huge number of textures? That may well be the problem. I explained somewhere else the other day that quake maps use a load of default textures supplied by the quake game and you don't have those in your little pk3 file. If you do have a copy of the game then you can take take the baseq.pk3 (something like that) file and load it into irrlicht and it should improve the number of textures loaded but may still not be enough (for some reason).
Unfortunately baseq.pk3 is effing huge so you can't distribute it (maybe not even legal too i don't know) but you can strip out any of the stuff you don't actually need from it to reduce the size.
Are you using irr 1.4? I think in this version there were vast improvements to the bsp loader and many more things were loaded from the maps that weren't before (though this could have been present in 1.3 as well).
The irrlicht one did used to have stuff missing from it, though not textures, possibly it was just a good one that had all its own textures or something.
It might also be that you're exceeding the single mesh poly limit(if quake maps load the objects as scene nodes).
Sorry if I'm wrong it's only a suggestion.