Ane, Looks to me like you have posted your server code (and not your "client code" as you have stated). You are associating the string "//ip_do_servidor/Server" with your server object. So the lookup string (that a client needs to use) will be:
where "host" is the name of the computer where the RMI server is running.
I have a feeling that perhaps you are having trouble understanding how RMI works. Allow me to recommend a series of tutorials on RMI that are available from the following Web page: