Poser has it's own runtime native runtime plus the Download runtime both located within the Poser folder, a hold over from pre-Vista days.  But Vista through Win 8.1 has security measures installed which prevent read/write access to any application installed in either Program Files or Program Files (x86).  As a workaround, SmithMicro upgraded Poser to optionally create a runtime folder in a share location away from Program Files so as to maintain functionality without reprogramming the core application.  Right now, yes, you will see multiple runtimes, however, your content should go into the share runtime, not the main runtime as you would perform for Poser 6. 

Your Win7 installation would follow the same rule before it died, there shouldn't be anything different.  For P6, try setting it's compatibility to an earlier OS.  Win 8 has a compatibility troubleshooter which might facilitate the process.  This feature can be found under the icon's properties panel.