Here's an extract from the FAQ...
In order to display an interactive board within a forum post you will need to enter the following code when writing your post:
(pgn]Your PGN Here[/pgn]
As an example, to view the Immortal Game, you would post this :
(pgn] [Event "Immortal game"] [Site "London"] [Date "1851.??.??"] [Round "?"] [White "Anderssen,A"] [Black "Kieseritzky,L"] [Result "1-0"] 1.e4 e5 2.f4 exf4 3.Bc4 Qh4+ 4.Kf1 b5 5.Bxb5 Nf6 6.Nf3 Qh6 7.d3 Nh5 8.Nh4 Qg5 9.Nf5 c6 10.g4 Nf6 11.Rg1 cxb5 12.h4 Qg6 13.h5 Qg5 14.Qf3 Ng8 15.Bxf4 Qf6 16.Nc3 Bc5 17.Nd5 Qxb2 18.Bd6 Qxa1+ 19.Ke2 Bxg1 20.e5 Na6 21.Nxg7+ Kd8 22.Qf6+ Nxf6 23.Be7+ 1-0 [/pgn]"
change the ( to a [ and it should post the pgn. I showed it that way to stop it actually posting a pgn.
hope that helps