He's done the same as Epic did for Magma, meaning he used vertex lighting to merge the textures on the rock/ lava meshes.
Lightmaps are your best friend with large and complex meshes like Fordy is using, as Static meshes look like crap when you light them at the best of times, so by adding a custom lightmap to the mesh you can give it the effect of being properly lit without having to worry that it'll look rubbish because of the bad way meshes are lit (vertex lighting sucks).
I haven't got a link to any lightmap tuts I'm afraid, but I'd say somewhere like 3DBuzz.com would have tuts, or do a Google for it
It's best to lay something like that out on paper with good and precise measurements so you've got something to work from in max. As long as you've got your grid set up correctly for the UT2003 scale, you shouldn't have any problems (that link I gave you has info on how to set this up, on the very first page).
And lastly, there's no such thing as 'visibility' in Max, not in the way you think (like the terrain tool in Ued), Fordy has simply cut out the section for the stairs to cut down the polys used in the map - no point having those polys there when they're being covered by another mesh
Two other good maps for you to look at are CTF-DE-ElecFields, and DM-Flux2; they're both build exclusively in max with very little BSP work and Flux has no terrain, even though it looks like it has, it's all meshes.
When starting something like that, it's good to plan ahead and know where you want to seperate the meshes, as a number of smaller meshes is a load easier to optimize than one big mesh would be.
