Oh when will some kind soul port the series to PPC? Please. Having said that, I like Grim Fandango even more.
As for Gilbert Goodmate, there is a PC version, too, but I played the PPC version. For the PC version, see
http://www.gilbertgoodmate.com/.
PPC version, here:
http://www.z-logics.com/.
Some more info, here:
http://www.pocketgear.com/software_detail.asp?id=12574
I think the PDA version works on PPC 2k2, 2k3, 2k3se. X3i should be fine. There should be a demo version somewhere, too.
If you play this, install it on a storage card and do yourself a favor; download and install the high quality speech and music files. They are worth it.