Personally, I've always started with the main text, using just a text editor (Vim, being my preference).

What I usually do (and I'll admit it seems archaic) is just put placeholders in the text where I'll need a picture/graphic or a code sample, and then add those later in whatever final tool I end up using for publishing the article (example: Windows Live Writer, for posting to my blog).

Works fine for me, because it lets me concentrate more on the text than on the format/appearance or whatever.