Problem with Icelandic special characters on Mac

Hello
I am working on a Flash publication for students, and I want it to run on Mac as well as PC. Everything goes fine, except a problem with three special characters in my language, Icelandic. I am working on a registration and login page where I am using text boxes and text input boxes. Everything looks correct on PC, but on Mac the characters Þ Ð Ý are lost.
I have tried different fonts etc.
Any idea what is wrong?
Jónas Helgason
