Check out 7-zip. http://www.7-zip.org/ It's a freeware zip app, that I have used in my own mel zipping utils. It can easily be fully command line driven. For example, to update a zip with a file at the command line is easy as:
7z u c:\temp\myzip.7z c:\temp\somefile.txt c:\bob\bob.txt
This will update myzip.7z with somefile.txt, and bob.txt
Plus 7zip can read winzip files, rar files, etc. Very nice!