||In case anyone is still looking for MapScan for Windows, which I think is a very handy program, you can get it at http://netgis.geo.uw.edu.pl/free/mapscan/. I think the site is at the University of Warsaw, but I'm not sure because I don't speak Polish. Anyway, the site works, unlike the official UN sites, and version 1.0 is still the current version.
MapScan is a beta that never got revisited, and it's a bit cranky. It's finicky about file formats, and it doesn't have command-line options or other things that would make it easier to use. However, it does turn line drawings into shapefiles, and that's something that no other free software that I know of will do.
I'm not sure if MapScan will work with JPEGs, because it likes for things to be more concrete than that. The best input for MapScan is a one-bit-per-pixel image, kind of like what you get if you "posterize" an image. You can use IrfanView (free for home use or US$10 for professional use) to convert images into TIFFs and reduce their color depth. IrfanView, by the way, is a wonderful piece of software that's useful for many things. Unfortunately, www.irfanview.com doesn't seem to be working as I write this. But with the combination of IrfanView and MapScan, you could deal with just about any format.
And by the way, for those of you who are interested in converting images from one file format to another, about the only format that IrfanView can't handle is MrSID. MrSID Viewer, which is free from LizardTech, will convert MrSIDs to TIFFs, and you can use IrfanView to proceed from there. It's very unlikely that anyone would need to vectorize anything that began as a MrSID file, but this stuff is useful for other things.