Is the server exporting the mount point via NFSv3 or NFSv2?
There is an issue with more recent RedHat based mount versions (since at least FC1) not falling back to trying NFSv2 if the NFSv3 mount fails.
Can you mount using '-o nfsvers=2' (using the CentOS4 mount binary)
interesting...
# mount -o nfsvers=2 /mnt/cvs/
works fine using the mount binary from the CentOS4 box -
thanks for that tip