Mac to Windows -- maybe text encoding

[Steve and Lee Ann Setzer]

I have a problem that I think is related to text encoding, and I'm looking
for suggestions.

Here is the issue:

(A) I wrote a HyperCard stack years ago to teach the International Phonetic
Alphabet to students using games.
(B) I used the excellent PalPhon font to display the IPA characters.
(C) This year I decided to port the stack to Mac OS X, and hopefully
Windows, using RunRev.
(D) I switched to a newer font, IPAPhon, built by the original author of
PalPhon. It comes in both Mac and Windows TrueType versions; since OS X can
use either format, I used the windows TTFs for maximum compatibility).
(E) I do all my work on a Mac running OS X, but I have access to RunRev for
Windows and a decent Windows 2000 PC.
(F) The games involve buttons that have IPA characters in their names
 (Inspector-->Text Formatting-->Font-->IPAPhon Roman)
(G) When I move the stack to Windows, many of the button names show the
wrong character, either a rectangle or just a different letter/glyph.

I've been rummaging around through this list's archives and also the RunRev
documentation, and I'm pretty sure this is related to the charSet property
or similar text encoding issue.

Is there a way to have the standalone use the MacOS encoding even when it's
on Windows? Or is there some kind of automated way to tell which characters
are going to "move" and automate the translation?

It's a fairly complex (and fragile) program, and my early experiments with
manually searching for the "wrong" characters and replacing them with the
"right" ones (using Windows Character Map to find the new locations) have
been error-prone, so I'm looking for something more reliable.

Thanks all,

Steve Setzer