It's because the archaic Daz installers are looking for Poser.exe rather than Poser2010's executable. Make an empty text file in your Poser directory or just outside the runtime you're trying to install it to and name it Poser.exe. It fools the installer and the figures will then install ;). For the gen 4 figures it's probably better if you install them to your main Poser runtime.

Laurie