Jane, it sounds like you're doing everything right so without looking at it there's no chance of determining what's wrong. There aren't, like, font declarations in the HTML as well as in the CSS are there?
As before, I'll take a look if you want me to. Maybe it just needs another pair of eyes.
Edit: I just sent you a nonsense-filled ePub with six different font embeddings. It works for me in EPUBReader (Firefox plugin), Adobe Digital Editions, Calibre, and Sigil. If it works for you as well, try to find what's different from yours. If mine doesn't work for you there's something fishy going on.
