To expand on your original question a little bit...

Gimp is a free image editing program similar to Photoshop. It's free.

Hexagon is another modeling program, not free, but very cheap as compared to other modeling programs...

Blender is another free modeling app. Extremely full featured and powerful, but if you haven't yet learned to model, I wouldn't start with Blender, but rather end with Blender ;o). It's complicated to use.

There are other programs out there that are useful if you make things for Poser: UVMapper, Roadkill (both uv layout programs and both free), Notepad++ (for editing text in some of Poser's files), Baum3D for making 3D trees (free), Ivy Generator for making 3D ivy (free), PoseRay (free) for file conversion and model adjustments, etc....

Laurie