The font could be corrupt.
If you haven't sone so already, I'd suggest searching to see if it's available in OpenType format. (I somehow doubt it since you're asking this question.)
Delete the font, and re download/purchase it from where you got it. If it's a free font, a lot of times you're getting what you paid for. Many (not all) free fonts are very poorly crafted. That may explain the compatibility issues with Leopard. Or it may simply be corrupt, and a reinstall of the font will solve your problems.
Another (rather convoluted) option would be to find a computer where the font works. Using either InDesign or Illustrator (or some sort of vector-editor), type the characters you need in a new document, convert them to outlines, and save them to use on your Mac as an EPS.
Last resort - if none of the above work, consider finding a new dingbat font.
