Heroes III on Mac OS X

Hi,

Can anyone help me on getting Heroes III run in the classic env. ?
I can start os 9 in X, do everything, run all apps, no problems.
But when I play Heroes III after some time playing it just crashes, the
game stops, the screen goes black and back to osx, then Heroes III is
still in the dock. I cannot quit it, and will only go away when I force
quit is several times. And only after doing that classic can be
stopped.
I did clean installs of mac os 9, used a disk image as play disk, used
a normal cd, ran classic from a system folder copied from a working os9
machine. Nothing works, situation is always the same. I can play for a
short time without any problems, but it always crashes after a short
time (but I have time enough to save the game, it's like after 5 mins
before it crashes)
If anyone can help me on this... Thanks