If they are materials for Poser, you do it the same way in the material room, only to the ground.

If they are just plain seamless tiles I believe you can still use them in the material room. Only you have to right click in the work space, pick "new node" and then "2D" and then "image_map" and then browse to the material.

I have several seamless floor tiles from archibase.com that I use that way.  You can adjust the size of the scaling that the tile is applied.

Or you can use them as flood fills when you are creating textures in your graphic program, or for web backgrounds etc.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi