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The /etc/exports file is used by both mountd and nfsd
format, /mnt/hardrive machinename(rw)
	/mnt/harddrive groupname(rw)

there are more options



man exports

EXAMPLE
       # sample /etc/exports file
       /               master(rw) trusty(rw,no_root_squash)
       /projects       proj*.local.domain(rw)
       /usr            *.local.domain(ro) @trusted(rw)
       /home/joe       pc001(rw,all_squash,anonuid=150,anongid=100)
       /pub            (ro,insecure,all_squash)
       /pub/private    (noaccess)

       The  first  line exports the entire filesystem to machines
       master and trusty.  In addition to write access,  all  uid
       squashing  is  turned  off for host trusty. The second and
       third entry show examples for wildcard hostnames and  net-
       groups  (this  is  the  entry `@trusted'). The fourth line
       shows the entry for the  PC/NFS  client  discussed  above.
       Line  5  exports the public FTP directory to every host in
       the  world,  executing  all  requests  under  the   nobody
       account.  The  insecure  option  in this entry also allows
       clients with NFS implementations that don't use a reserved
       port  for NFS. The last line denies all NFS clients access
       to the private directory.


	Root squashing is when root logs into a remote machine,
it's UID is reduced to nobody unless specified otherwise in 
the /etc/exports file.
The following is a E-mail note from MFromm about root squash.


/       crystal(rw) lexor(rw) mercury(rw) ohura(ro,no_root_squash) tina2(rw) sulu(rw)


This allows these machines to read/write with normal UID mapping, root
gets changed to nobody, except for ohura, which mounts ReadOnly and
can read files as root.

/etc/exports