LTSP-5 is a complete re-design of LTSP. It is tightly integrated with Linux distributions, so that you don't have to download it from us. You'll only need to install the packages that your favorite distro provides for you.
LTSP-4.2 is OLD. We definitely recommend that you use LTSP-5.
If you really need LTSP-4.2, take a look at LTSP-42 for more info. If all you need is being able to run older hardware as thin clients, ALT Linux 4.0 Terminal might come handy for Pentium/16M or better.