Races of Faerûn has some nice info about lycantrhopes. It might even be possible to play an afflicted character with the original alignment, but that will mean that you'll lose control of that character periodically, and the party has to go to ground and restrain you.
This is assuming you fight the curse all the time. If you give in to it even once, your alignment will change irrevocably (baring the usual wish-work, but that's not something you run into at every street corner).
I think the DM will shamelessly use this as a plot-hook. The next session, maybe even sessions, will involve looking for the cure post-haste (there is not much time before it becomes incurable).
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I reiterate: talk to your DM. He's the only sure source you have. He might alter the rules about this, and all we can tell you out of our books is null and void. He might already have planned things about it. He might give you at least some info. He might want you to wriggle like a bait on the proverbial hook.