You should be able to use ~np~ tags (no processing) to include code in forum postings. The closing "no processing" tag should have a forward slash just like HTML tags.
In the above example did you also "close" the "Module" plugin?
You could also try:
(which assumes you've set up an RSS feed of your blog. I can't quite remember how the IDs for that work, whether they map to individual object IDs or not, you'll have to experiment with that one a little bit.)
As for the forums, I suppose you could try the RSS feed trick with that too.
It sounds like you really want to embed those features into one page so perhaps the templating is the way to go, in which case then the syntax would probably not be the same, since it's not quite the same thing. I'm not sure who's the template expert around here but I will defer to them whomever they are.