I don't work in Illustrator that much, so I can't tell you how to go about placing the various colours/objects on their own layer, but I can tell you how to get teriffic raster-to-vector conversion:
Go here (vectormagic.com) and look around the site for info and directions. I stumbled upon this site about a year ago. I have another program that I use for most my coversions (that program does a good job for the, usually simple, file conversions I require), but when I have something intricate or graphically complicated, I rely on vectormagic and get phenomenal results.
More that likely, you're going to want to choose to output your bitmap/raster file to .eps and then open that in Illustrator.
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