Kizarvexis said:
I did it like this. An old ranger going out to sea gets a letter from Valen. As the ranger wanders around the galaxy he/she inevidently runs across the human who wants to be the ranger. He trains the would-be-ranger and gives him his robes, denn'bok and a letter when he dies. Role playing opportunities for when the human ranger meets Minbari are endless. The knowledge of the human ranger about his mentor and the letter should win out in the end with other rangers, but the Warror caste ought to be a pain for a long while.
Of course, you could just tell the player 'no, you have to be a Minbari ranger until late season two, then humans can join.'
Kizarvexis
I'd have to echo your last comment, Kizarvexis, at least for any games I run.
I do like your idea - I'd work it that the human was asked to return the Denn'bok, cloak and Isil'zha back to the Ranger training compound in Tuzanor. I wouldn't let the player join the Anla'shok at that point, but their behaviour would be worth a hefty bonus to Ranger influence. Depending on how the character got there, I might also give a minor increase to one of the Minbari relevant influences.
The character might also be asked to pass any useful information on the Rangers, but I'd probably draw the line there. Things would change when Sinclair begins the process of recruiting humans and non-Warrior Caste Minbari into the Rangers. With a history of such honourable actions, (and a nice Ranger influence to boot) the character concerned's name would naturally float up to the top of the list.
As for a Human becoming a Ranger before Sinclair's arrival, I don't think that there's much fluff to support that idea at this point. As the Rangers at that time were, for the most part, also members of the Warrior Caste, I wouldn't fancy that Human's chances of not having a fatal 'accident', courtesy of the Warrior Caste. Sinclair's arrival on Minbari, and the mass resignation of most of the Warrior Caste members of the Anla'shok, would change this though.
Of course, that's just my opinion, and no more valid than anyone elses. What constitutes gaming canon is in the hands of the Games Master concerned.
Chobbly