Check the registry for the known install date of a Windows system and output via InputBox (for easy copying). I never thought I'd be thankful for having learned Visual Basic a decade ago...

windows_install_date.vbs

Dim shell, val, regKey

On Error Resume Next

' UNIX time of OS installation
regKey = "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\InstallDate"

' Invoke WScript and read the key
Set shell = CreateObject("WScript.Shell")
val = shell.RegRead(regKey)

' If an error was found then set "Not Found" otherwise set the found install date
If err.number <> 0 Then
	readFromRegistry = "Not Found"
Else
	readFromRegistry = val
End If

' Clean up
Set shell = Nothing

' And output to screen using InputBox, so it can be easily copied
Call InputBox("Install Date", "Windows Install Date", readFromRegistry)