There is an existing account under your IP address, "Zon Trennick". If this is yours, you can use the Lost Password feature to have a new password sent to your e-mail address. If this is not yours, you need to register as multis with other players sharing your internet connection.
Ah. You cannot create an account for another player; he will need to register himself from his own connection, and he should have no trouble getting the account approved that way. If the two of you ever share a connection, you will need to register as multis.