By the way, here's what I did while running this project head first into a dead-end:
(Click for a slightly bigger version)
Some of the steps (click for big):
First I've created the composition in Photoshop with characters and objects rendered in 3dsmax (and some photos, like the sky and the ocean), which already took quite a while. The next step was basically tracing the image with a pencil, although it sounds more easy than it was. The third image shows the whole thing further down the process, with the pencil drawing color corrected and highlights drawn in as well. I've also added some artificial grain, to fake more detail and blend the pencil lines a bit better. Coloring is mostly based on the initial comp, with a few tweaks. As a finishing touch some brush strokes are overlayed and the credits and logo added.
When I started this project I actually wanted to do a poster for each ToMI-episode, but after realizing how much work it was (even though I did use three finished 3D-characters from my other poster), I still have to think about that