If u don't pay any money for RHEL, you will not have the following services:
1. No support if u face any problems.
2. No updates are available for free download.
But if don't need the above services, u can download and work with RHEL for free and for unlimited period of time.
Try CentoS .. it's RHEL .. you can download it for free from www.centos.org .. you will also be able to download updates for free and get all the support for free ..
I use it myself and it works pretty fine ..