Everything should still work, but the textures might not be what you'd expect. They'll have to be optimized for PoserPro 2010 ;o). Poser 4 had a very simple node setup: IIRC, only specular, reflection, bump and diffuse (it's been a long while...lol). The materials have been greatly expanded as has the lighting.

What are your system specs? Processor, RAM, etc?

Laurie