This is very, very difficult. Many people imagine that there are programs that will simply convert pictures into fonts for them. This is not the case; most fonts are painstakingly created by drawing curves that closely approximate the letterforms. In addition, special rules (which improve hinting, etc.) mandate that these curves be drawn in specific ways. Even designing, or merely digitizing, a simple font can take hundreds of hours.
Given that, there are two major programs used for font design on the Macintosh, Fontographer ($280) and FontStudio ($400). These programs will allow you to import scanned images, and then trace them with drawing tools. The programs will then generate type 1, 3, TrueType and Bitmap fonts for either the Macintosh or the IBM PC. They will also generate automatic hinting. They also open previously constructed outline fonts, allowing them to be modified, or converted into another format.
As far as I know, there are no shareware programs that allow you to generate outline fonts.