Some other web-based communities I use have links to HTML summaries, which generally pop-up a new window (note of course that these aren't the evil auto-popups, but only appear when you click :-). I've heard people say they find those useful, because they can have the second window off to the side while they compose.

Perhaps a combination of ideas: start people at the point of having the summary, with a link to the page that covers the HTML usage in depth (separate window or not, at your judgement). Have that be the default for unreg users, and for registered users at Level 1. At Level 2, go to just the link (or a briefer summary, like a simple list of tags for visual aid/recognition/reminder, plus the link). At Level 3, reduce again (if you didn't go with just the link at L2, now you would, or you'd go completely bare). That also answers the issue of when to move from one state to the next. When I registered as a user and started replying to posts, it didn't take long to move from L1 to L2, so the "annoyance" factor for the more seasoned users should be low.

--rjray