I have experienced the problem of converting windows to mac.
We needed Word files for Mac 8.5 so what I did was the following:
First convert the text to rtf, then parse the rtf with a matrix I
composed from the official codepages you find here
http://unicode.org/Public/MAPPINGS/VENDORS/APPLE/
I used this approach because there was something wrong with the
conversion in Word for Windows.
CE languages showed corrupted characters.
After I wrote the conversion tool, the files were ok for mac.
The text is plain ASCII so I suggest you have a look at the codepages
on the link I gave you
and do a hex dump of your file (rename it to a .bin file for example)
in Visual Studio so you can trace wrong characters.
Maybe then you can find out which code page has been used. If the
approach with the .NET codepages doesnt work
you can still use the matrix method,
Hope this helps,
Joachim