I modified the "forum_posts.asp" at line 865 to add the following:
'Display Facebook like option if not a private forum
if intcatid <> 2 then
dim strmyurl
strmyurl= strForumPath & "forum_posts.asp?TID=" & lngTopicID
response.write("  <script src=""http://connect.facebook.net/en_US/all.js#xfbml=1""></script><fb:like href=""" & strmyurl & """ show_faces=""false"" width=""40"" font=""arial""></fb:like>")
end if
Intcatid value specifies the category of the forum which is private - you dont want people facebooking your private forum posts. Even though the public shouldnt be able to get to them, its not a good idea to bring a bunch of traffic beating on the private sections. The code in blue above is one long line, but in this forum post format it gets line-wrapped. Also, if your forum uses dark colors, you will want to insert the following
[space]colorscheme=""dark""
immediately after ...arial"" and before > in the blue text above to ensure that the facebook text is readable, otherwise you will have black text on black background.
The result looks like the following:

When you "like" a post, you get a little popup to enter "comments" that will be included in the facebook wall-post. After you submit the facebook like, it will show "for you" that you have liked the post, and your facebook wall will show the link and post title etc.
How this works is described
here on Facebook.I hope someone finds this useful......