I think that their should be some help at the top of the postings area. You could even have it only pop up when is user is below a level. Cuz I am pretty sure most people once they get to level 2 or so know how to do it. Also they could put the <code> put code here </code> inside of the text area that we have to put data into.
Maybe even put the code tags into the text area so that all they have to do is get the insertion point in the right place. I suppose it is all a matter of getting the balance right -easy for first timers but without annoying the more experienced users.
I think there is an assumption that people are comfortable with this type of HTMLish structure that perhaps has never been challenged.