Man!... hope some one here can help... Could be your graphics card, need driver updates, a different sort or something... I've been playing with Poser 7 since the 13th  and it runs like a dream for me, and my pc is half that of yours. Just one problem opening one render I saved, the skin has fallen off the bones...and bits of the skelleton are sticking out all over. It's a right mess, no idea how that happened or why.

I've been playing with maybe 20 or so different new items in poser 7, saved maybe as many, and that one is the only one that caused a problem. No crashes, freezes or otherwise for me. And the render times! WOW... so fast!... AND!... the amount of figures, clothing, props etc Poser 7 can cope with makes Poser 6 look how Windows Paint is compared to Photoshop!

Good luck