Quote - Do I drag and drop files from one app to the other ?
Or can i just drag and drop the entire runtime into the Poser8 runtime as is ?

Do not do this, you'll almost certainly break P8 by overwriting newer versions of vital files with older ones. > Quote - Or do you mean create some sort of link from Poser6 to Poser8 ?

Use the "Add Library" button and the navigate to your P6 install (see various threads and/or the manual for details).