Habe es übrigens nun so gelöst, über Outlook.
Public Sub ReadOtherUserAppointment()
Dim objolApp As New Outlook.Application
Dim objNS As Outlook.NameSpace
Dim objRecip As Outlook.Recipient
Dim objFolder As Outlook.MAPIFolder
Dim UserName As String = "s.mustermann"
objNS = objolApp.GetNamespace("MAPI")
objRecip = objNS.CreateRecipient(UserName)
objRecip.Resolve()
If objRecip.Resolved Then
objFolder = objNS.GetSharedDefaultFolder(objRecip, _
Outlook.OlDefaultFolders.olFolderCalendar)
For i As Integer = 1 To objFolder.Items.Count
'For example...
MsgBox(objFolder.Items.Item(i).Subject)
MsgBox(objFolder.Items.Item(i).Start)
Next
End If
End Sub
Nur möglich, wenn der Benutzer seinen Kalender mit einem 'shared'.