I don't know a whole lot about MACs or how they implement virtual pc but it seems to me like the game can't find the CD that you are supposed to have in the drive when you start the game.Make sure in Windows 98 if you double-cick on "my computer" and then the cd-rom drive that you can browse the Wizardry 8 #3 CD that should be in your CD-ROM drive.
Always remember the Tleilaxu Epigram:
Here lies a toppled god
his fall was but a small one
we did but build his pedestal
a narrow and a tall one.