Actually, think I've seen that restriction on RHEL3 mentioned somewhere on LQ before. You might want use the LQ search fn to follow up.
In any case, RHEL 3 is old... and due to run out of support in 1 yr http://www.redhat.com/security/updates/errata/
Highly recommend you get latest RHEL 5.4, much longer support and more capability.
Of course, if you want free, Centos is the same code for free. 5.4 should be out by now or very soon.