.Net Zip library
The MSDN blogs are a really great source for all sorts of information. I browse the main blog page regularly, just to get a feeling of what is happening on the Microsoft side of things. This morning I found a link to a Codeplex project which encapsulates the System.IO.Compression.DeflateStream class to allow you to read and write zip files.
The project can be found here: http://www.codeplex.com/DotNetZip.