Problem on my G5 with "Hexen for Mac"

Hello,

I bought "Hexen for Mac" and find that as the character moves, the
screen does not change with the movement in time, as in, you'll take a
step forward and a quarter of the screen moves with you and another
quarter shows only what you saw a step earlier (Get It? It's weird).

I am running the game on my G5 that defaults to OS X, but the game
opens in OS 9.

Any help?

Thanks,

aiiiiee