>From .NET, is there an existing class that would allow me to zip a file?

The following seems to work like a charm:

Imports System.IO

Namespace Framework

    Public Class Zip

        Public cDestinationFile As String = ""
        Public cSourceFolder As String = ""
        Public cError As String = ""
        Public cFile As String = ""
        Private oFile As Collection = New Collection()
        Private oApp As Framework.App
        Private oProcess As Framework.LXProcess

        ' This is when we access the data provider in desktop and Web service mode
        Public Sub New(ByVal toApplication As Framework.App)
            oApp = toApplication
        End Sub

        ' This is when we access the data provider in desktop and Web service mode
        Public Sub New(ByVal toProcess As Framework.LXProcess)
            oProcess = toProcess
            oApp = oProcess.oApp
        End Sub

        ' Zip a file
        Public Function Zip() As Boolean
            Dim lcFile As String = ""
            Dim llOK As Boolean = False
            Dim loByte(21) As Byte
            Dim loObject As Object
            Dim loDestinationFolder As Shell32.Folder
            Dim loFile As Shell32.FolderItem
            Dim loShellClass As Shell32.ShellClass = New Shell32.ShellClass
            Dim loSourceFolder As Shell32.Folder

            Try

                ' If the source folder does not exist
                If Not oApp.DirectoryExist(cSourceFolder) Then
                    cError = "The directory " + cSourceFolder + " does not exist."
                    Exit Try
                End If

                loSourceFolder = loShellClass.NameSpace(cSourceFolder)

                loByte(0) = 80 : loByte(1) = 75 : loByte(2) = 5 : loByte(3) = 6

                ' Make an empty PKZip file
                File.WriteAllBytes(cDestinationFile, loByte)

                loDestinationFolder = loShellClass.NameSpace(cDestinationFile)

                ' For each file
                For Each loObject In oFile
                    lcFile = loObject(1)

                    ' If the file does not exist
                    If Not oApp.FileExist(cSourceFolder + "\" + lcFile) Then
                        cError = "The file " + cSourceFolder + "\" + lcFile + " does not exist."

                        ' Remove the temporary file
                        If Not oApp.DeleteFile(cDestinationFile) Then

                        End If

                        Exit Try
                    End If

                    loFile = loSourceFolder.Items.Item(lcFile)
                    loDestinationFolder.CopyHere(loFile, 20)
                Next

                llOK = True
            Catch loError As Exception
                cError = loError.Message
            End Try

            Return llOK
        End Function

        ' Add a file
        ' expC1 File name
        Public Function AddFile(ByVal tcFile As String) As Boolean
            Dim loObject(1) As Object

            loObject(1) = tcFile

            oFile.Add(loObject)
            Return True
        End Function

    End Class

End Namespace

To initiate:

        Dim loZip As Framework.Framework.Zip = New Framework.Framework.Zip(oApp)

        loZip.cSourceFolder = "d:\"
        loZip.AddFile("Server.docx")
        loZip.AddFile("Test.jpg")
        loZip.cDestinationFile = "d:\Test\Test.zip"
        If Not loZip.Zip() Then
            MessageBox.Show("Error: " + loZip.cError)
            Exit Sub
        End If

It makes use of the Shell to accomplish. This is a very fast and fully compliant with the shell extension as installed with WinZip.