I'd like to render an orthographic view of each of four walls in a small room full of furniture, with the lighting and shadows of the full room.  Is there a way to make the furniture invisible but still have it cast shadows?  I want to wind up with a lightmap to use on each wall to fake the long-rendered real lights.  Or is there a better way to light a room quickly?

Set each light to depth-mapped shadows.
Enable the menu item Render/Reuse Shadow Maps.
Render your scene.
Hide every prop and figure in the room.
Render it again. The shadows will be there but no props or figures will be visible.

But then you'd have to make a render that could be used as a UV mapped texture on the walls. I suppose that's possible, but sounds very tedious.

Is the ultimate goal to produce props to be rendered in real time in another app, such as a game?

Because if the goal is just to render faster in Poser, then just re-use the shadow maps. This is why they exist - to save rendering time.

You can check the box in render settings for "shadows only" and save as png

Thanks.  Im using ISF lighting in a train compartment and making two versions of the carriage, one high res one low for distant shots.  To save render time on the low res version I want to be able to light the cars fast; I thought I'd use the regular shaders on the low res objects, and apply a lightmap to the emissive channel.

Is there any way to export the shadow maps?  Are they stored in a temp cache while rendering so I could get them directly?

Quote - Is there any way to export the shadow maps?  Are they stored in a temp cache while rendering so I could get them directly?

I've seen them as .shm files in the same folder as the scene, but I don't know the format.

I can't think of a simple way to "bake" in the lighting.

I imagine you're going to say more requirements that will make this suggestion pointless, such as you want to animate from different viewpoints, but here goes.

Make the side of the rail car invisible.

Render one compartment, centered in the preview. Save the render as an image.

Load that render onto a one-sided square, connecting it to Alternate_Diffuse and turn off Specular_Value and Diffuse_Value (set to 0). Position the square just inside a window, maybe 8 to 12 inches back, so we see it from outside. Now you can re-render from slightly different camera angles, but they can't be too far from the original angle. Once that looks about right, duplicate the square for the other 7 compartments.

This will work for limited perspectives. If you render several sets from slightly different angles, you should be able to populate even a curved train of many cars - using different angles for each car. 

 Hm. How about simply placing some squares inside the compartments and put ambient on them. It wouldn't cast shadows of course, but the windows would appear lit.

Perhaps even put the ambient on the windows (thinking aloud here) so the glass "glows" - it would be for dark scenes only anyway - in daylight you can't see the lights inside a train (even if it's on) - I work in trains so I've seen them quite a lot LOL