Thanks to Gwyneth's responses to my previous post, I've managed to get Poser 6 working on 10.4.2.

Briefly, do an "Archive and Install" from the Tiger install DVD, making sure that the option to keep existing users is selected. Run the 10.4.2 combo updater. Then do the normal Software Update shuffle, and manually add the bits & pieces that didn't transfer over from your previous install -- I had to reinstall Little Snitch, Pith Helmet, Applejack, a third-party Japanese input method, etc. Everything else was functional from my old OS install. And Poser now runs!

The process does work, and is less impractical (it's mostly automatic anyway) than it is simply...insane...to have to do this much to coax any app to run! (: But, y'know, it works, so hey!

Since the useful responses are attached to my 1-star post, I'll leave that there and post this as a new review: 4 stars to balance out to 2.5, since re-installing the OS is not a reasonable requirement for running any app. When they eventually correct this rather wacky problem I'll delete these two posts and re-rate it on its own.

But Poser is working now, and is rather fun!