firewall rules for torrents

[Gary Aitken]

Can someone point me to or fill me in on what's required in the way of firewall
rules for torrent operation?

I gather I can configure for a given listening port,
and my existing outgoing rules should cover outgoing conversations.
But it's unclear to me whether or not the protocol is statefull from inside
the firewall (i.e. "ipfw ... setup keep-state" rules for outgoing packets 
would cover it), or whether the download ports need to be opened up because 
the a conversation may be initiated by an external peer.

Thanks,

Gary