rhel5 is a bit old ,but it is supported so
What version is it ?
RHEL 5.9 is the current in the older 5 series
Also seeing as RHEL is a commercial operating system you MUST have a paid for "license"
as in the required support contract and register the install with red hat
being a server class OS rhel is rather "manual" in configuring the network and NFS
please reread the redhat documents
https://access.redhat.com/knowledge/...erprise_Linux/
the docs for rhel5 are at the bottom of the page
and have a search through the knowledge base
https://access.redhat.com/search/quick
( most hits will require you logging into the red hat website with the username you set up with the subscription )