The Problem
You want a TrueType font that's being used by one of your Windows-using coworkers, but you're using a Macintosh.
The Spin
This is a particularly vexing problem because it needn't have been an issue at all. TrueType fonts were designed to be self-contained and portable, and ought to be trivially cross-platform as well.
Windows stores TrueType fonts in flat files which have a .TTF extension. Rather than treat these portable gems as a special case - fonts and suitcases have always been strange ducks with slightly different behaviors than files and folders - the Macintosh world wants to use it's data-and-resources file structure. So the TrueType data is placed in 'sfnt' resources and be identified as a font by a 'FOND' resource.
The Solution
TTConverter, by Chris Reed, elegantly converts TrueType fonts between the two operating systems.