How do I convert a suitcase font?
Font Suitcases can potentially hold 2 different kinds of fonts: bitmap fonts and TrueType fonts. Normally, font suitcases that hold bitmap font data are only one half of the font; to be usable you need to have the additional PostScript Outline font files (these will have an LWFN icon).

Otherwise, the font suitcase can represent a TrueType font, which compared to a "PostScript Type 1 Font Suitcase", is truly self-contained.

I'm not aware of command-line font converters for the Mac. The only type of conversion I could imagine using command line tools would be converting from a resource-fork-based Font Suitcase to a Datafork TrueType font (.dfont), and possibly from a Mac TrueType to a Windows TrueType font (basically you'd need to extract the 'sfnt' resource entries).

To try to figure out if the Mac Font Suitcase is a TrueType font, you can use the following command:

grep -c sfnt /Library/Fonts/BankGothic/..namedfork/rsrc


What this does is return the number of times 'sfnt' is found in the resource fork of the file in question. If this returns 0, the file is most likely not a TrueType font.

Note that by default, terminal command will only act on the data fork part of files. For example:

ls -la /Library/Fonts/BankGothic
-rw-rw-r--@ 1 root  admin  0 Mar  7  2007 /Library/Fonts/BankGothic


This shows that the file is empty (has a file size of 0). To specifically target the resource fork, you append /..namedfork/rsrc to the filename as in the following example:

ls -la /Library/Fonts/BankGothic/..namedfork/rsrc
-rw-rw-r--  1 root  admin  346937 Mar  7  2007 /Library/Fonts/BankGothic/..namedfork/rsrc


EDIT:
If it is a Mac TrueType font, I can convert it to one or more Windows TrueType fonts (.ttf) for you. (For this particular type of conversion, there's no need to use font software; a simple Mac resource editor (and knowledge of this process) should be sufficient. If I do convert it in this manner, I'll provide screenshots of what I'm doing for the record).

EDIT 2: See my answer on StackOverflow for "Using OS 9 resource fork fonts with CSS" for a tool I wrote that would allow drag and drop extracting of sfnt resource entries to individual ttf font files.