Windows 7 and 10
You can just install CNCcomp and it shall work as it is. Windows 7 and 10 comes with "Windows Installer 4.5" and "Microsoft .NET Framework Version 4.0". - so all necessary is included.
Windows XP and Vista
When you double-click CNCcomp.msi file, it shall launch a Windows Installer. But if you receive a message about unknown file type, you need first to install "Windows Installer 4.5". You can download it from Microsoft at: http://www.microsoft.com/downloads
CNCcomp runs on "Microsoft .NET Framework Version 4.0" and thus also it must be installed. If CNCcomp doesn't start, you most probably haven't yet installed .NET Framework. Please go to Microsoft Windows Update and install "Microsoft .NET Framework Version 4.0".
Windows 95 and 2000
CNCcomp 4.6 doesn't run on Windows 2000 or 95. Please use older CNCcomp 4.4 on those platforms.