strComputer = "."
Set objSWbemServices = GetObject("winmgmts:\\" & strComputer & "\root\cimv2")
Set objOS = objSWbemServices.ExecQuery("SELECT * FROM Win32_OperatingSystem")
For Each strOS in objOS
 dtmInstallDate = strOS.InstallDate
 strReturn = WMIDateStringToDate(dtmInstallDate)
 Echo strReturn
Next
Function WMIDateStringToDate(dtmInstallDate)
 WMIDateStringToDate = CDate(Mid(dtmInstallDate, 5, 2) & "/" & _
 Mid(dtmInstallDate, 7, 2) & "/" & Left(dtmInstallDate, 4) _
 & " " & Mid (dtmInstallDate, 9, 2) & ":" & _
 Mid(dtmInstallDate, 11, 2) & ":" & Mid(dtmInstallDate, _
 13, 2))
End Function