The best zip/unzip utility for .NET that i've experienced so far is DotNetZip. It is a third party class library that you can reference in your project.
You can download DotNetZip here:
http://download.codeplex.com/Download?ProjectName=dotnetzip&DownloadId=258012&FileTime=129571576121970000&Build=18207
Extract it to a directory on your pc. You add the DLL (ionic.zip.dll) to your project (
you add it as reference) and then you can zip files within a directory, just like this:
'Set filename to save your new zip file
Dim zipFileName As String = "C:\MyZipFile.zip"
'Set the path to directory containing the files you want to zip
Dim fileNames As String() = Directory.GetFiles ("C:\User\Name\Document\FilesToZip\")
Using zip As Ionic.Zip.ZipFile = New Ionic.Zip.ZipFile
'Add all the files in that directory to zip
For Each file In fileNames
zip.AddFile(file)
Next
'save the newly created zip file in the path you specified above
zip.Save (zipFileName)
End Using
hope it helps.
Best Regards.