Hi,

Would it be possible to (easily?) modify the code to allow HTML in posts in certain circumstances.

No, it isn't and I belive, there is no demand.

and then be able to actually show what it does.

And how do you handle css or/and javascript conflicts? And how do you handle tags outside of your restrictive-list (<a> <strong> <em> <div> <span> <img> <p> <h1> <h2> <h3>)?

HTML *is* the language of the Web ...

... and BB is an accepted standard for a forum or board.

regards
Micha