don't know if you've worked it out and i'm still a poser n00b but on my rather bad image attached, click on the library icon (1) and then click on the arrow thing (2) and at the bottom it says 'add new runtime' - click that and go and find where your studio content folder is stored on your puter and select that. actually after doing that image i noticed if you use the + button at the bottom right it also allows you to add a runtime.

you can also add the poser 6 runtime to D|S - got to edit>preferences>directories> where it says D|S content directories click on that and select poser content directories, go to add and got to where you've got poser 6 stored on your puter.  e.g on my puter it is c:program filese frontierposer 6.  just select the poser 6 folder, don't use the runtime folder.  and hit accept to complete. 

um as i said i'm a poser n00b so someone correct me if i'm wrong.