Fanfiction.net forbids anything with a rating above PG-13.
Also, I'm not sure about HP message boards, but they may also have Nfic on them--I've just never been on one.
"You take turns, advise and protect one another, even heal or be healed when the going gets too tough. I know! That's not a game--that's friendship!" ~Shelly Mezzanoble, Confessions of a Part-Time Sorceress: A Girl's Guide to the Dungeons & Dragons Game