Here are some links and tips that I hope will be helpful.  Most people produce toon pictures using shaders (Estherau mentioned Olivier's Art Materials, but there are others available here and at CP) or by using the "cartoon with outline" mode and rendering in Preview mode.  I'm mostly interested in creating line art, and I found the following to be extremely helpful:

http://www.renderosity.com/news.php?viewStory=13559

And here's a tutorial on creating anime-style renders:

http://www.renderosity.com/mod/tutorial/index.php?print=66

And here's a more recent one on using Photoshop and other 2D programs to do the postwork:

http://www.silverblades-suitcase.com/tutorials/htm/17.html

Another possibility is to set up your materials in Poser using the Toon Materials wacro, turn all the light/dark materials in the toon node to white or black, and then fiddle with the toon ID settings so that Poser will draw the outlines where you want them.  My avatar image was done with this technique, but it takes a long time to set up the figures and create new material zones with the grouping editor.  I'm not sure it was worth the effort.

One final tip:  vectorizing your image using a program like Adobe Illustrator or CorelDraw will make the lines look smoother and more attractive.