Most of the time, if th author is considerate, the folder extracted from a zip will be a runtime folder which should go into the Poser main folder.  If you follow jester's suggestion about unzipping in a special folder, the contents can be transferred folder by folder or the entire runtime folder can be mover to the Poser folder.  But do not move it into the Poser runtime folder, you will never see the content.  Transfer to the Poser folder, you will see an overwrite warning, just click yes.  You will not lose anything, but the new content will be deposited into its new home in the right places (hopefully).