Para obtener el nombre de máquina de un ordenador del que conocemos la dirección IP emplearemos la función GetHostNameFromIP que se describe más abajo.

Private Const WSADescription_Len = 256
Private Const WSASYS_Status_Len = 128
Private Const WS_VERSION_REQD As Long = &H101
Private Const IP_SUCCESS As Long = 0
Private Const SOCKET_ERROR As Long = -1
Private Const AF_INET = 2

Private Type WSADATA
  wVersion As Integer
  wHighVersion As Integer
  szDescription(0 To WSADescription_Len) As Byte
  szSystemStatus(0 To WSASYS_Status_Len) As Byte
  imaxsockets As Integer
  imaxudp As Integer
  lpszvenderinfo As Long
End Type

Private Declare Function WSAStartup Lib "wsock32.dll" _
  (ByVal VersionReq As Long, _
   WSADataReturn As WSADATA) As Long

Private Declare Function WSACleanup Lib "wsock32.dll" () As Long

Private Declare Function inet_addr Lib "wsock32.dll" _
  (ByVal s As String) As Long

Private Declare Function gethostbyaddr Lib "wsock32.dll" _
  (haddr As Long, _
   ByVal hnlen As Long, _
   ByVal addrtype As Long) As Long

Private Declare Sub CopyMemory Lib "kernel32" _
   Alias "RtlMoveMemory" _
  (xDest As Any, _
   xSource As Any, _
   ByVal nbytes As Long)

Private Declare Function lstrlen Lib "kernel32" _
   Alias "lstrlenA" _
  (lpString As Any) As Long

Public Sub SocketsCleanup()
   If WSACleanup() <> 0 Then
       MsgBox "Ha ocurrido un error en los sockets.", vbExclamation
   End If
End Sub

Public Function SocketsInitialize() As Boolean
   Dim WSAD As WSADATA

   SocketsInitialize = WSAStartup(WS_VERSION_REQD, WSAD) = IP_SUCCESS
End Function

Public Function GetHostNameFromIP(ByVal sAddress As String) As String

   Dim ptrHosent As Long
   Dim hAddress As Long
   Dim nbytes As Long

   If SocketsInitialize() Then
     'convertir la cadena a un long
      hAddress = inet_addr(sAddress)
      If hAddress <> SOCKET_ERROR Then
        'obtener un puntero a la estructura HOSTENT que contiene el nombre
        'y la dirección correspondiente a la dirección dada
         ptrHosent = gethostbyaddr(hAddress, 4, AF_INET)
         If ptrHosent <> 0 Then
            CopyMemory ptrHosent, ByVal ptrHosent, 4
            nbytes = lstrlen(ByVal ptrHosent)
            If nbytes > 0 Then
               sAddress = Space$(nbytes)
               CopyMemory ByVal sAddress, ByVal ptrHosent, nbytes
               GetHostNameFromIP = sAddress
            End If
        Else
            MsgBox "Falló la llamada a gethostbyaddr."
        End If
        SocketsCleanup
      Else
        MsgBox "Dirección IP inválida."
      End If

   Else
        MsgBox "Fallo en la inicialización de los sockets."
   End If
End Function