in red hat you DO NOT install the gcc compiler alone and without the "autotools" and 5 dose not use the 4.6 compiler
the rhel5 series i believe was locked with the gcc 4.1 installed ( 4.3 might be in the updates ? )
use "yum" to install software from the RHN software repo
that is the repo you got access to with the REQUIRED support contract
--- rhel is NOT free ---
Also is there a NEED to ,as in a MUST USE, the old 5 ( 5.what ? 5.8 is the current in the 5 series) ? The current RHEL release is 6.2
--- then from that list install the development tools --
yum groupinstall "Development Tools" "Development Libraries"
BUT you MUST have a paid for support contract to install software
- depending on the install disk a OLD and NOT updated gcc might be on the install dvd
also see the red hat support - you ARE paying for it so you might want to use it .