RedHat Enterprise Linux is not free - it is only available from Redhat, and you have to pay.
You can get Centos, which is exactly the same, just without the Redhat trademarks.
Depending on what your intended usage is, RHEL or Centos may be a bit old since they are intended for stability rather than cutting edge. You can get Centos from www.centos.org
If you like Redhat, then you may like to consider Fedora which is the successor to the "free" Redhat distros like RH9. The current version is Fedora Core 6. Alternatively, distros such as Ubuntu may be a good choice.
I hope this helps