While I wouldnt recommend trying to go Van Goh in Flash, you can still create moderately detailed vector artwork using the Pen Tool
, much in the same way that you might in Adobe Illustrator--with the added advantage of being able to animate it. You can start from scratch in Flash, or build on top of a rough sketch; I prefer to build from a sketch like the one above, because while I love in my graphics tablet in Photoshop or Painter...it drives me buggy in Flash, and seems to hinder more than help.
The sketch is nothing special and requires no preliminary preparation or post-scanning adjustments; its just mechanical pencil on copy paper, a cheerful little pixie-boy that randomly popped into my head. I saved it as a JPEG image after scanning.
Lets move on to turn that pile of pencil scribbles and smudges into clean line art.