I can't help much with the problems you are having getting the Mac versions of things to install.  I have Poser 8 and Vue 8 installed on my Mac and had no problems with the installations, or any problems installing content (other than some of the Daz installers being so old that the code they were written in is no longer supported on the latest Mac OS).

As far as Poser slowing to a crawl on the Windows side, I think that part of your problem is the fact that it is being run in a virtual machine.  VMWare Fusion is good if you are using Windows for simple tasks like word processing, etc.  But if you are going to be doing very resource intensive tasks like 3D work or gaming, it is not so good.  The best option is to use bootcamp to partition the drive and dual boot Windows and OS X.  When using a VM, you are sharing the cpu, RAM, etc. between two OS's and neither is getting the full use of the machine.  If you did a true dual boot, Windows would then have full access to the hardware and your programs would run much better.  In a VM, the OS only has access to a limited amount of virtual resources...not the actual hardware.