I've never seen that syntax before.
Assuming the server does have an NFS mount available, I would do something like the following. Either become root to execute these, or preface each command with sudo
mount -t nfs -r hostname.example.com:/INSTALL/RHEL5.1_x86_64 /mnt/rhel
Now the remote directory is mounted at /mnt/rhel (an arbitrary mount point).
Check man mount
for more information.