In a recent project I had to grab an attachment from a POP box and then unzip the attachment.

I found an unzipping product called 7zip, it’s open source and there’s a command line version.  See their downloads page for the commandline version - http://www.7-zip.org/download.html

Once you have this exe on your server you can easily unzip a file using the following code:

dim pathToZip as string = "c:\some\folder\file.zip"
Dim p As Process = Process.Start("C:\Program Files\7Zip\7za.exe", "e " & pathToZip & " -oc:\")
p.WaitForExit()

Obviously you are not limited to just unzipping, you can do anything the command line version does: zip, password protect a zip file, list the contents, etc