For Sale: codswallop ( Charlie Z Harris - crazygill85@hotmail.co.uk ) defrauding people

Slander is verbal, if the comment is written it is a libel :)
That depends on whether the subject of the comment is engaged in the online conversation.

[Bulletin board posts] are rather like contributions to a casual conversation (the analogy sometimes being drawn with people chatting in a bar) which people simply note before moving on; they are often uninhibited, casual and ill thought out. Those who participate know this and expect a certain amount of repartee or 'give and take'.

When considered in the context of defamation law, therefore, communications of this kind are much more akin to slanders (this cause of action being nowadays relatively rare) than to the usual, more permanent kind of communications found in libel actions. People do not often take a 'thread' and go through it as a whole like a newspaper article. They tend to read the remarks, make their own contributions if they feel inclined, and think no more about it.

IANAL, however, and it's probably best to avoid any defamatory / actionable comments.