Yeah. I think I'm doing something wrong. ... lol :-)
Update: well, the vertex data seems correct, at least. I'll need to check that I'm using the correct mesh definitions.
Update: the face data is also correct. So I'm probably doing something wrong when trying to use vertex arrays...
Update: figured out my problem. I was using the "firstVertex" value as if it were a byte offset into the vertices, when it was really saying "the n-th vertex". I.e. I had to multiply it with the size of a vertex to get the real offset in bytes. So now it's looking much better... except for the psychedelic colours. :-) That's not a mistake though. I'm just not using the textures yet.
PS. This tutorial is quite helpful if you're considering of trying this for yourself.