If you have Poser 10 or higher then you can use the grouping tool. It got a complete revamp in Poser 10. That's what I use for most of my grouping work. For small areas that are hard to see/get to with Poser's crap-tastic cameras (and their inability to focus on a specific area of a non-rigged model), use blender to assign materials, but that's really only necessary if you're doing things like eyes and teeth.

Here is a video I did earlier this year all about the grouping tool.

https://www.youtube.com/watch?v=A1IdI7ZsXKI