Ei, I have figured out!
I'm a complete newbie, but i figured that ubuntu comes with a built in firewall (iptables), have start to read some tutorials and understanding chains and policies. but in the mean time i fount out that firestarter is a frontend to configure iptables, so i've manage to allow ftp / ssh.
I'm gonna need to understand better iptables for the future, so do you know a good tutorial or documentation?
I just cant access from an external IP to the server. Any Info ?