"PP2010 is now refusing to save to library unless I am running the program as an admin, but comparing with crashes, I'd think that's a minor issue."

Vista or Win7? if so, thats an easy one.. UAC. (UAC is designed to protect the Program Files area from damage. part of which is preventing writing to the PF areas ad-hoc, which is basically what Poser does. fixes are to disable UAC, Modify UAC, Run as Admin, Install Content to a non PF Runtime or just install Poser outside the Program Files folder)