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
the docs for rhel5 are at the bottom of the page
and have a search through the knowledge base
( most hits will require you logging into the red hat website with the username you set up with the subscription )