I'm not sure why things check out properly in nifskope and then don't appear at all in the GECK (save the bounding box), but my night-long struggle ends in defeat. Is it something wrong with the http://www.fallout3nexus.com/downloads/file.php?id=14500

We'll need a bit more information on the meshes in order to help you out here. Did you give the meshes a UV Map? Did you make NormalMaps for the textures?

I didn't make the mesh at all; I found it on Nexus as a modder's resource. It has the .nifs and a texture map but for any more detailed answers you'll have to http://www.fallout3nexus.com/downloads/file.php?id=14500 yourself. Since the only 3d work I've done was years and years ago, all I can say is that it shows up in nifskope (with textures) but not the GECK.

I had a look and noticed two problems with the meshes:
1. No textures are included at all, which means they'll have to be made from scratch.
2. The .NIF versions are too old to be used in FO3. They'll have to be opened by, and re-exported from, some 3d editing software before they can be used in FO3 or FO:NV.

I've optimised and retextured the model now, exported with the latest NIFTools for Fallout 3's settings. I tried to add collision as shown in http://www.fallout3nexus.com/articles/article.php?id=290 but the (red) collision part shows up 15degrees offset from the model itself in NifSkope. Offset collision or not, unfortunately nothing shows in the GECK. I tried using http://www.fallout3nexus.com/articles/article.php?id=248 as well to no avail. Is there something else I am missing?

I've uploaded my work to http://www.mediafire.com/?u1xdy0lb75fbii7 , including textures, exported .nifs and the mother .3ds file if you would like to take a look at it for problems. Any help is greatly appreciated!

read my comments that are on that collision tutorial. imo setting a static collision up like that is entirely a waste of time. just add a bhkcollisionmodifier to the collision shape and it's set up and ready for export. the collproxy is actually rarely used. as 99% of the time you will be creating an optimised collision mesh, not simply cloning the real time geometry to act as the collision shape.

that model isn't worth using in its current state imo. especially with the high poly collision shape, the dozen or so mesh objects that should not be separate mesh objects, the mess that is its face normals etc

but anyway you are missing 2 things and an incorrect shader setup. the root node Needs to be a BSFadeNode not a NiNode. you do not have any normal maps. and you have sf_shadow_map and sf_shadow_frustum enabled which you shouldn't.