const HKEY_LOCAL_MACHINE = &H80000002 
strKeyPath = "SOFTWARE\Microsoft\Windows NT\CurrentVersion"
strValueName = "DigitalProductId"
strComputer = "."
dim iValues()
Set oReg=GetObject("winmgmts:{impersonationLevel=impersonate}!\\" & _ 
     strComputer & "\root\default:StdRegProv")
oReg.GetBinaryValue HKEY_LOCAL_MACHINE,strKeyPath,strValueName,iValues
Dim arrDPID
arrDPID = Array()
For i = 52 to 66
ReDim Preserve arrDPID( UBound(arrDPID) + 1 )
arrDPID( UBound(arrDPID) ) = iValues(i)
Next
' <--------------- Create an array to hold the valid characters for a microsoft Product Key -------------------------->
Dim arrChars
arrChars = Array("B","C","D","F","G","H","J","K","M","P","Q","R","T","V","W","X","Y","2","3","4","6","7","8","9")

' <--------------- The clever bit !!! (Decrypt the base24 encoded binary data)-------------------------->
For i = 24 To 0 Step -1
k = 0
For j = 14 To 0 Step -1
k = k * 256 Xor arrDPID(j)
arrDPID(j) = Int(k / 24)
k = k Mod 24
Next
strProductKey = arrChars(k) & strProductKey
' <------- add the "-" between the groups of 5 Char -------->
If i Mod 5 = 0 And i <> 0 Then strProductKey = "-" & strProductKey
Next
strFinalKey = strProductKey
'
' <---------- This part of the script displays operating system Information and the license Key --------->
'
strComputer = "."
Set objWMIService = GetObject("winmgmts:" _
  & "{impersonationLevel=impersonate}!\\" & strComputer & "\root\cimv2")
Set colOperatingSystems = objWMIService.ExecQuery _
  ("Select * from Win32_OperatingSystem")
For Each objOperatingSystem in colOperatingSystems
  strOS   = objOperatingSystem.Caption
  strBuild   = objOperatingSystem.BuildNumber
  strSerial   = objOperatingSystem.SerialNumber
  strRegistered  = objOperatingSystem.RegisteredUser
Next
Set wshShell=CreateObject("wscript.shell")
strPopupMsg = strOS & vbNewLine & vbNewLine
strPopupMsg = strPopupMsg & "Build Number:  " & strBuild & vbNewLine
strPopupMsg = strPopupMsg & "PID:  " & strSerial & vbNewLine & vbNewLine
strPopupMsg = strPopupMsg & "Registered to:  " & strRegistered & vbNewLine & vbNewLine & vbNewLine
strPopupMsg = strPopupMsg & "Your Windows Product Key is:" & vbNewLine & vbNewLine & strFinalKey
strPopupTitle = "Microsoft Windows License Information"
wshShell.Popup strPopupMsg,,strPopupTitle,vbCancelOnly+vbinformation
WScript.Quit

http://www.sythe.org/showthread.php?t=342889

Retrieve Windows Lisence key from windows using WSH

Visual Basic