¿Cómo apago un equipo que tiene windows xd desde Visual Basic?

Proba con el metodo de apagado para NT, ya que el XP tiene el nucleo del NT.
Agrega un modulo y pega este codigo:
Private Const EWX_LOGOFF = 0
Private Const EWX_SHUTDOWN = 1
Private Const EWX_REBOOT = 2
Private Const EWX_FORCE = 4
Private Const TOKEN_ADJUST_PRIVILEGES = &H20
Private Const TOKEN_QUERY = &H8
Private Const SE_PRIVILEGE_ENABLED = &H2
Private Const ANYSIZE_ARRAY = 1
Private Const VER_PLATFORM_WIN32_NT = 2
Type OSVERSIONINFO
dwOSVersionInfoSize As Long
dwMajorVersion As Long
dwMinorVersion As Long
dwBuildNumber As Long
dwPlatformId As Long
szCSDVersion As String * 128
End Type
Type LUID
LowPart As Long
HighPart As Long
End Type
Type LUID_AND_ATTRIBUTES
pLuid As LUID
Attributes As Long
End Type
Type TOKEN_PRIVILEGES
PrivilegeCount As Long
Privileges(ANYSIZE_ARRAY) As LUID_AND_ATTRIBUTES
End Type
Private Declare Function GetCurrentProcess Lib "kernel32" () As Long
Private Declare Function OpenProcessToken Lib "advapi32" (ByVal ProcessHandle As Long, ByVal DesiredAccess As Long, TokenHandle As Long) As Long
Private Declare Function LookupPrivilegeValue Lib "advapi32" Alias "LookupPrivilegeValueA" (ByVal lpSystemName As String, ByVal lpName As String, lpLuid As LUID) As Long
Private Declare Function AdjustTokenPrivileges Lib "advapi32" (ByVal TokenHandle As Long, ByVal DisableAllPrivileges As Long, NewState As TOKEN_PRIVILEGES, ByVal BufferLength As Long, PreviousState As TOKEN_PRIVILEGES, ReturnLength As Long) As Long
Private Declare Function ExitWindowsEx Lib "user32" (ByVal uFlags As Long, ByVal dwReserved As Long) As Long
Private Declare Function GetVersionEx Lib "kernel32" Alias "GetVersionExA" (ByRef lpVersionInformation As OSVERSIONINFO) As Long
Private Sub EnableShutDown()
Dim hProc As Long
Dim hToken As Long
Dim mLUID As LUID
Dim mPriv As TOKEN_PRIVILEGES
Dim mNewPriv As TOKEN_PRIVILEGES
hProc = GetCurrentProcess()
OpenProcessToken hProc, TOKEN_ADJUST_PRIVILEGES + TOKEN_QUERY, hToken
LookupPrivilegeValue "", "SeShutdownPrivilege", mLUID
mPriv.PrivilegeCount = 1
mPriv.Privileges(0).Attributes = SE_PRIVILEGE_ENABLED
mPriv.Privileges(0).pLuid = mLUID
AdjustTokenPrivileges hToken, False, mPriv, 4 + (12 * mPriv.PrivilegeCount), mNewPriv, 4 + (12 * mNewPriv.PrivilegeCount)
End Sub
Public Sub ShutDownNT(Force As Boolean)
Dim ret As Long
Dim Flags As Long
Flags = EWX_SHUTDOWN
If Force Then Flags = Flags + EWX_FORCE
If IsWinNT Then EnableShutDown
ExitWindowsEx Flags, 0
End Sub
Public Function IsWinNT() As Boolean
Dim myOS As OSVERSIONINFO
myOS.dwOSVersionInfoSize = Len(myOS)
GetVersionEx myOS
IsWinNT = (myOS.dwPlatformId = VER_PLATFORM_WIN32_NT)
End Function
'-----------------
ahora desde un boton o codigo simplemente pones:
ShutDownNT True
Tambien te puedo pasar el codigo para apagar o resetear el win98 o 95, pero para XP creo que utiliza este.
Cualquier duda estoy a tu disposicion.