I vote for "no postwork" (except maybe the text). One, most contests and challenges allow postwork, so this would be different. Two, it's a Poser challenge, not an art contest. The point, IMO, is what you can do with Poser, not what you can do with Photoshop. And it's just a challenge - no prizes or anything. If someone cheats and uses postwork, big deal - they're only cheating themselves.

Ascinct, there's plenty of free clothing and hair available. Poser comes with several hair props. Koz and Studio Maya offer free hair that's better than most of the hair being sold. If you're not using a popular figure like V3, clothing is more difficult, but dynamic clothing can be easily fit to any character.