PRE-inclusion of ‘html’ into the edit form…

hello to everybody,
I need a little hack, and also need help doing it.
this is the ‘mission’:

when I write a new post (or page, it doesn’t matter), I click on ‘Write’ > ‘Post’ and the system shows me a emplty form where I can edit my post and place my everything.

ok, what I want is the form must already show some ‘html’, for example the table I’m using to edit the content or some images that appear on every post…

is it possible? how?

thank you in advance for any suggesion!