NFS setting error in Ubuntu 8.10

[loody]

Dear all:
I sudo apt-get install nfs-kernel-server, nfs-user-server and nfs-common.
After config /etc/exports as I need, I execute "nfs-kernel-server
restart", but I cannot see any message show out.
then I execute "showmount -e localhost" and I cannot see any files shared out.

below are my outputs:
# /etc/init.d/nfs-kernel-server restart
# showmount -e localhost
portmap getport: RPC: Success
#

if I execute "nfs-user-server restart", I can see my sharing folders as below:
# /etc/init.d/nfs-user-server restart
Stopping NFS servers: mountd nfsd.
Starting NFS servers: nfsd mountd.
# showmount -e localhost
Export list for localhost:
/media/test_NFS      *
#

but I cannot mount it from another Ubuntu.
my questions are:
1. what is difference between "nfs-kernel-server" and "nfs-user-server"?
2. why my nfs-kernel-server doesn't show anything? did I miss something?
3. are there any additional commands or packages can help me to find
out what's wrong?
appreciate your help,
miloody