Вы можете использовать CoCreateGuid API-функция
Declare Function CoCreateGuid Lib "ole32" (ByRef GUID As Byte) As Long
Public Function CreateGUID()
Dim ID(0 To 15) As Byte
Dim N As Long
Dim GUID As String
Dim Res As Long
Res = CoCreateGuid(ID(0))
For N = 0 To 15
GUID = GUID & IIf(ID(N) < 16, "0", "") & Hex$(ID(N))
Next N
CreateGUID = GUID
End Function