Use WIN32 Function directly : DLL « Windows « VB.Net Tutorial

1. VB.Net Tutorial
2. Windows
3. DLL

Option Strict On

Public Module Tester

   Public Declare Unicode Function MessageBox Lib "User32.dll" Alias "MessageBoxW" (ByVal hWnd As IntPtr, ByVal lpText As String, _
          byVal lpCaption As String, ByVal uType As UShort) As Short

   Private Declare Unicode Function GetSystemDirectory Lib "kernel32.dll" Alias "GetSystemDirectoryW" _
           (ByVal lpBuffer As String, ByVal nSize As Integer) As Integer

   Private Const MB_OK As Integer = &H0&
   Private Const MAX_LEN As Integer = 256

   Public Sub Main()
      Dim caption As String = "System Directory"
      Dim message As String
      Dim buffer As String = Space(MAX_LEN)
      Dim retChars As Integer

      retChars = GetSystemDirectory(buffer, Len(buffer))
      message = Left(buffer, retChars)

      MessageBox(Nothing, message, caption, MB_OK)
   End Sub
End Module