I did not find a command-line Zip utility on my 770. FBReader probably uses a library, rather than an external command, to handle Zip files. However, I did find a site that had a precompiled command-line binary of UnRar for ARM Linux platforms (like the iPaq, for example), so just for kicks I installed in /usr/bin on my 770. It seemed to work fine. So, assuming you have some basic Linux knowledge, it probably won't be too hard to find a compatible utility for Zip, even if you're not comfortable compiling your own software.