The TutsPlus.com site has a tutorial posted showing how to make use of the ZIP functionality in PHP to handle the compression and decompression of ZIP archives programatically.

Compressing files when transferring them over the internet has a lot of advantages. In most cases, the combined total size of all the files in the compressed format comes down by a nice margin. This means that you will save some of your bandwidth, and users will also get faster download speeds.

[...] One factor that can discourage you from compressing files or make the process very tiresome is the fact that you might be doing it manually. Luckily, PHP comes with a lot of extensions that deal specifically with file compression and extraction. You can use the functions available in these extensions to automatically compress files in PHP.

This tutorial will teach you how to zip and unzip (compress and extract) files to and from a zip archive in PHP. You will also learn how to delete or rename files in an archive without extracting them first.

The tutorial starts with the compression of files making use of the ZipArchive class to create a new instance, add files to compress and close it out to write the resulting archive. Next it shows the reverse, using the same class to create an instance and extraction path. There's also an example of using a loop for even more control of which files are included in the archive.