There are not very interesting NVidia cards in "Mac World" for PowerPC host.
MorphOS at the moment has a good 3D support for ATI cards; give a look at these tests http://amiga.ikirsector.it/forum/viewtopic.php?f=40&t=13185
It's better to continue to concentrate on ATI 3D (and 2D).
In MorphOS 2.6 there is now also a support for ATI9600/9700; I hope to see in next months:
-1) "speed up" in 3D (as seen in some video about Bigfoot's MacMini, months ago).
-2) the full support 2D of ATI 9800/9700/9600 and the same about the 3D for these cards.
(Note that We have now powerful and very cheap PowerMac G4 supported and other interesting models G4 (MacMini/Emac/Powerbook/Ibook...), and one day if needed, the G5 Systems AGP and PCIe)

((I hope that with the support of very cheap PowerMac G4 (and in some cases very powerful) We' ll have many new users and developers))

regards

[ Edited by Divinity on 2010/10/23 12:47 ]