Configure client:

Log in as root (you can use another user though): 

# cd ~
# ssh-keygen -t dsa
don't add a password

# scp .ssh/id_dsa.pub root@server:/root/

Log in on the server

If nescessary:
# mkdir .ssh
# chmod 700 .ssh

Then continue:
# cat id_dsa.pub >> .ssh/authorized_keys
# rm -f ~/id_dsa.pub

Log in to the client again.  Use rsync to sync a directory. This copies all file in the tmp dir to the tmp dir on the remote host:
# rsync -avu --delete -e ssh /tmp/ root@server:/tmp

-a archive
-u overwrite newer files on the server
-v verbose
-z compressed sending of the files, handy when you have a slow connection like an analoge phone line.
-- delete delete files on the receiving host that don't exist on the client side.