I just looked this up (and can't find it now) but someone mentioned this:

Open up the Poser 7.ini file in notepad.
It can be found under documents and settings/(your profile name)/application data/Poser 7
Find teh line
PREVIEW_OGL_OBJECT_BBOXPICKING 0
and change the 0 on the end to a 1.

It may help, but I'm slowly getting teh feeling that the fault has to do with the ATI card and drivers themselves.