You'll need a 64-bit compatible version of a zip/unzip tool that allows you to run it from the command line. Be warned that not all your users will have 64-bit systems so you need to find a solution that works with 32 and 64-bit systems. The old pkzip/pkunzip utilities were 16-bit DOS (command line only) apps which is why they may not work properly on your 64-bit system, although the WOW (Windows on Windows) layer should kick in when you try to start one of those old applications. Alternatives compression utilities you can try are 7-zip or winrar.