digital cameras

I have little experience with Polaroid since the '60's when I occasonally used a Polaroid back for my 4x5 (9x12 cm) Linhof. Since then I've only used Polaroid for 'scope pictures. However, what I do recall is that while they're OK for use as full-scale snapshots, the film is too grainy for enlargement. I learned about this when I used the negative film from Polaroid. I've concluded that the quality of the photos from this technology is not as high as what's wanted by users of digital photography in general, i.e. I doubt it's up to the quality of the 640x480 resolution of the Sony cameras. My interest in digital photography has been stimulated by the need to integrate photographs into technical documents and correspondence. There's plenty of software for rendering the color photos as what they are, up to "glossy-paper-magazine" e.g. Time or Spiegel but once you start to enlarge the image, the lack of resolution becomes a major factor. I've considered other image processing approaches, e.g. scan-rate conversion software which reduces a raster image to Fourier series in both directions, thereby allowing you to "fit" the image to whatever resolution you like, though it requires post-processing to straighten and sharpen edges, etc. What really puzzles me is whether it can process and render a photo as black and white line-art. Anyone have experience with this? Dick