You cannot register RH8 for the same reason you cannot expect to activate Windows 1.0, It is very OLD. To give you an idea, RH9 mas the last in the Redhat GNU/Linuxes, to be followed by fedora core 1, which can be thought of as RH10 (only not exactly). The fedora project is up to #8 with 9 around the corner... so that would be like RH17, you see?
Though you do not need to activate linux to use it (this is one of the freedoms you are granted as part of the GNU GPL) you should be using a more up to date OS.
There are a great many distros to choose from. Here is a website to help you.
If I may ask, what made you pick RH8 anyway?