Egg - Dover is Dover Publications. They reprint historical books and a huge selection of royalty-free artwork for designers. Much of the latter is available on CD-ROMs (they seem not yet to have embraced DVD).

Handrawn, a lot of Dover electronic art is very low res, mainly small TIFF files. Each jaggy in the original is translated into a point by tracing. And, no tracing program today is going to create logical polynomes (e.g., leaf, blossom petal, pistel, stamen...). The latter would make it easier to apply colors and fills to appropriate sections.

It's not difficult to trace in Xara using zoom and Pen or Shape Editor, though it takes time. That said, the coloration ideas earlier in this thread are useful if vectorization is not all that important.