Looks to me like [MS]Win32/4.0 is the system that AS compiled the binaries on (since Config.pm is created during compile for the purpose of recording such information). Because Win32 binaries are compatible across Windows versions this means that relying on that is misleading.

However, the shell command 'ver' on my machine emits "Microsoft Windows 2000 [Version 5.00.2195]", so if you need more granular information about which Windows version you are running on, you might try that.