Thank you very much everyone for your feedback!

I'll respond here to your suggestions, and then offer a partial possible cause of the problem that I think I've located at the end, here. If what I think is happening makes any sense and anyone knows how to correct it, I'd be most grateful! If what I'm saying makes no sense, I'd also appreciate being told, to save me even more time barking up the wrong tree!

I apologize for any lack of clarity in explaining my issue: being somewhat new to Poser means that maybe I don't know exactly what need to be specified when explaining what's going on. I've made every object in the scene "invisible" by clicking all of the "visibility" options in the "Properties" of the Parameters window.so that they are unchecked ("Visible", "Visible In Raytracing", "Casts Shadows", all not checked). This makes them disappear from the Preview window (and, as far as I can tell, from the possibility of being rendered).

I've tried rendering in both Poser 4 and FireFly modes, and the problem is the same in each.

When rendering, I am looking at the scene through the Main Camera, and not one of the other ones (although none of the other cameras are obstructed by buildings, either, because I've made all of the other buildings other than the one I need for the scene invisible, as explained above).

The wall that raven has suggested I make invisible is part of the same Object as the building the figure is standing in front of, so when I make it invisible, she winds up standing in front of nothing - removing it DOES solve the problem of the blank wall render, but my figure is now rendered almost entirely off-screen again, as in my second post above.

I have had a little insight, I think, but I have no idea how to correct it. Hopefully one of you helpful folks can point me in the right direction:

At this time, I think that the issue has something to do with the camera's focal settings. In trying to rectify the problem, I've been playing around with just about everything, and it seems like the initial problem of the blank wall and the second problem of the central object of the Preview window being rendered off-screen are the same problem. Poser seems to be rendering things to the LEFT of what I'm actually looking at in the Preview screen (so the blank wall being rendered isn't something directly between the camera and the central figure - it's the wall to the left of the camera.). If I re-set the Main Camera's focal length to 38, then I get a render fairly close to what I'm seeing in the Preview screen (except for that stupid "fish-eye" effect). When I increase the Focal Length, my figure gets rendered to the right of screen.

I'll post 2 examples, with the building behind the figure made invisible and the Focal Length at 70, and we can see the problem.

I'm not sure why changing the Focal Length would make Poser render as if the camera was at a different angle... if that is the problem, is there a fix?

Thank you to anyone who has applied any of their time to helping me with this one. If I'm right, then hopefully the answer is close....

I've been working on this one issue for 12 hours now and I'm still unable to reach a resolution. I've scoured all of the documentation I can find, and I am completely lost. I'm not sure if the lack of response here (84 thread views, but only 1 response) indicates that everyone else is stumped or that I'm an idiot and whatever the issue is is beneath being addressed.... but it's driving me bonkers.

I've made practically everything in the scene not visible except the character (and her props and what-not) and the building behind her, and still that same, blank render. I don't see how the issue could possibly be that the camera is inside a building or behind a wall. I am throwing myself at the mercy of all of you. I have a short window of time to get this project completed, and picked up Poser because the ease of having human figures ready-made and easily-modified was too good to pass up, but I'm starting to wonder if I wouldn't have been better off sculpting a character in full in Blender (or whatever).

Again, any assistance that anyone might provide in explaining how to fix this is greatly appreciated.
Thank you.

ARGH! In an attempt to fix the fact that Poser was rendering from a completely different angle than what as shown in the Preview window, I started moving the camera around to try to get it to render the right area, and now I'm back at the original problem, again: the renders are just of blank space.

I can't figure out how to attach more than one file at a time to these posts, so I'm going to post a few pictures to give you all an idea of my camera placement and the contents of the Preview and Render windows, so hopefully someone can assist me, here. I'd really appreciate it. I've been up all night (morning, I guess, really, since I started around 4 a.m.) and I don't know why I've hit this snag or what to do about it.

However, if I can trouble you again, the render is still not quite correct. In the Preview window, my character is centred in the screen.. In the render, you can kind of make part of her out on the far right, there. Is there an explanation for this? In "Preview Dimensions", I set Width 600 and Height 300. In "Render Dimensions" I had clicked "Match Preview Window". Is there a similarly simple reason for this new disparity that I'm missing again?

Thank you for the continued suggestions: as I get comfortable with Poser (if I ever do), I will be sure to consider breaking things up into related groups.

As I get to grips with this thing, you guys may be hearing more desparate whining from me in the future, so get prepared...

THANK YOU THANK YOU!

That did the trick! I have no freaking idea how everyone else in the world managed to figure out all that file-moving-around... I hope to Jebuz not all the content I download is that involved!

Thank you again: much, much appreciated!

Thank  you for your response.

The Readme file begins with this:

"Long Hair Evolution  for DAZ-3d  Victoria 1-3  by kozaburo

Installation:
Copy the contents of the 'LongHair_evo_V1-3_PC' directory that you have unzipped
directly into your Poser directory.

File location:
Runtime:Geometries:hair:koz_long_evo.obj"

I assume this is what you're asking about? I'm not sure how this helps me locate it: There is no Library folder called "Geometries" that I can find within Poser, and the file is not located in the "Hair" folder anywhere.

If I misunderstand where exactly I'm supposed to be looking, please clarify. I do appreciate the help!

Thank you for the suggestion - it reminded me that Poser sometimes places things where one might not intuitively expect them to be. However, after checking the Figures folder, I was unable to locate it. I checked all of the folders thoroughly (I think) and still no luck.

Surely it must be SOMEwhere, no?