I have used Strepla, SeeYou, WindPilot 3D, and Great Plains Flight
Simulator, and other 3D intensive applications on Mac's for quite
awhile now.

If you buy a new Mac, you can usually get Parallels for about $10
more, if you buy them together. You can get Bootcamp free from Apple.

When running under Bootcamp, you will see native PC speeds. When
running under Parallels, the 3D speeds are slower than on a PC.
Parallels 3.0 (just released last week), is supposed to allow native
speeds for OpenGL and DirectX.

Unfortunately, when I ran Parallels 3.0, it would crash when running
SeeYou in 3D. WinPilot 3D became graphically unstable. When I
lowered the hardware graphics acceleration in Windows XP to the next
to the lowest setting, it would then run correctly, but then the 3D
graphics speed was no better than before.