[DllImport("user32.dll", SetLastError = true, CharSet= CharSet.Auto)]
public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);
VB Signature:
Private Declare Function MessageBox Lib "user32.dll" Alias "MessageBoxA" (ByVal hWnd As Long, ByVal lpText As String, ByVal lpCaption As String, ByVal uType As Long) As Long