@ Esther, on PC's zipped files will open in a separate window, or browser, no automatic unzip.  Now, if Winzip is installed, the application might initiate an unzipping protocol.  I use WinRAR and that app will always open the zipped file when I use the Open With command from the right-click menu.  Otherwise, Windows XP builtin zip program will always open into another window upon double-clicking.