Hmm. It still won't freeze no matter what I do. I did run into some glitches in main menu though. Sometimes the buttons stop working. Mouse works fine, menu music plays, but none of the buttons do anything. I have to shutdown dosbox. And when I run the game second time, it works fine. Strange.
If the problem is not within the image itself, it could probably be something with the files. I posted md5 hashes of my old Heroes CD on pastebin. If you check them with your installation, maybe we can find some differences. http://pastebin.com/J6jR6LtJ
The paths won't probably correspond and you should also replace backslashes with regular since you're on mac, but I think you can handle that. :)
Drop a note if you find anything, perhaps it will put us on a right track.