seeing as you are using the VERY old rhel 5.1 ( the current is 6.0 - or 5.6 for the 5 series )
i take it YOU DO have a EXTENDED LIFE contract with red hat ( one of the VERY expensive ones ) so that you can install the "backported" security updates and fixes
ask red hat that is why you are paying them a large bit of cash for support on that 5.1 server
if you DO NOT have a long extended life contract with red hat -- then DO NOT use it !!!
install the current CentOS 5.5
cent is the community "supported" version of RHEL