I wasn’t able to find the kind of wall and floor prop that I was looking for.

Would I be able to use images that I already have by laying them horizontally to create the floor, or vertically to make the wall? If yes, how can I do this? 

If you only want the surface showing, ie not showing any wall thickness, use the hires plane from the poser primitives folder, and then apply the image you want to it in the material room, you may have to tweak it if it has a particular pattern on it, you can then rotate it for your walls and floors.

It doesn't have to show any thickness because I just want to create a picture, and that part wont show.

Where is the poser primitives folder located? How can I use the hires plane?

Primitives are in the Props folder.  The Hires Plane can be loaded and positioned where you want it.  When it's in place, go to the Material room and attach the image you want to use.

I use the One Sided Square when I make a quick room because it reduces the poly count dramatically. You can get amazing results if you use Displacement, transparency and all the other bells and whistles.  It enables you to make details that look as if they're modelled in, rather than just painted on, add windows and/or doors, glowing parts and even lights.  If your version of Poser supports IDL, the lights will even work like real ones.

Good, innit?  

 

When applying an image to a HiRes Plane, set your X,Y scale to the exact dimensions of your image resolution.  For example, if your image is 600 X 800 pixels, scale the plane 600 on the Y and 800 on the X.  Then scale the entire plane to whatever size you like.  The purpose to follow this rule is to keep the image sharp and the perspective ratio correct.

Also, setting the Filtering to 'Crisp' for the Image Map helps the sharpness a lot.

The above image is basically a cube with texture and bump maps applied. It is a freebie at www.ontarget3d.com.

A quick IDL render set up using one infinite light and Bagginsbill's envirosphere. the objects in the scene are the one sided square primitive for the wall and a one sided high resolution plane for the ground. also a few low poly plant freebies to add a little visual accent.

No RT shadows, almost no specularity on the materials in this example. You can get pretty nice results with good textures and a displacement map (in this case a photoshop image adjusted version of the diffuse texture image) used in this manner...  terrific results if you spend the time setting up your lights and materials.

My one suggestion that might add to the comments already stated would be to visit the various texture specific websites for free to use textures and begin the process of building yourself a categorized library of image resources. You'll find it to be invaluable.

It seems complicated but I should learn better once I test out your suggestions.

Thank you very much!

bigglobe, "I wasn’t able to find the kind of wall and floor prop that I was looking for"

So you haven' found you P.I.C.K. (Poser Indoor Creation Kit) yet?
read about it here,
http://forumarchive.daz3d.com/viewtopic.php?t=156759&view=next

pick up a free version here,
http://www.yurdigital.com/catalog/3d-content/poser/pick

Invaluable and indispensable.