Depends on how the zip was packed. The "standard" is to have the Poser folder as the root. If this is the case one should unpack to the Poser folder, or if a remote runtime then the directory immediately above runtime.

For a tutorial on how to pack zip files for Poser see:-
http://www.philc.net/WinZip_tutorial2.htm

For a tutorial on how to unpack zip files for Poser see:-
http://www.philc.net/WinZip_tutorial.htm

For a free utility to install Poser zip files see:-
http://www.philc.net/unzip.htm

Hope this helps.