Whilst I think doing this native in Poser, using a variant of BB's Artistic Lens technique would be cool... :)

...applying these type of effects is probably what post production is all about, fundamentally.

You can use a Z-Depth render to provide a selection mask for different scene elements.

I usually find I have to adjust the contrast / levels of the Z-Depth layer, once its in Photoshop, to get enough detail into it, so easily select different scene parts.

CS5 that I have has vignetting and similar options in its factory supplied filters.

BB's thread on vignetting within Poser is worth revisiting though I expect... he directed me to it when I was looking to make a working magnifying glass lens recently...