You can do other things while rendering, but you're taking a chance. It's really glitchy, slow, and unstable. Poser will often lock up, unless it's a really simple render.

No so with dual processors, real or virtual. It's very stable, if slower.

At least, earlier versions of Poser are slower with hyperthreading. (Because they aren't written to take advantage of hyperthreading.) Poser 6 is supposedly not slower. It's not faster, either, but it's not slower.