connecting 2 machine via internet

Hi, I need to establish a secure connection between 2 machines (running Suse9.1pro) via Internet. I have a server machine, with a static ip address while the client is behind a modem/router/ADSL which has its own static/dynamic IP and performs NAT translation. client (192.168.0.x) ----- NAT/ADSL(Router static ip) ---- Server (Suse9.1pro with static IP) My final purpose is to be able to login on the client suse box. I also would like to support multiple clients and the connection on client side should be established without user intervention. I am evaluating vtun a the moment. Do you have any suggestion ? Thanks Ciao Giovanni