Are you using .NET 3.5? You could use the ZipPackage
class and related classes. Its more than just zipping up a file list because it wants a MIME type for each file you add. It might do what you want.
I'm currently using these classes for a similar problem to archive several related files into a single file for download. We use a file extension to associate the download file with our desktop app. One small problem we ran into was that its not possible to just use a third-party tool like 7-zip to create the zip files because the client side code can't open it -- ZipPackage adds a hidden file describing the content type of each component file and cannot open a zip file if that content type file is missing.