As for emulators, Richard Bannister has a whole suite of emulators for OS X. They generally run quite well - my iBook has no issues with running any of them.
However, he charges for such features as controller support and -- get this -- fullscreening the emulator. This would be fine if he coded the emulators himself, but... the large part of the emulators were coded by others, and Bannister just crippled them to try to cash in with Emulator Enhancer. If you absolutely HAVE to use one of his emulators, well, I hope you like being nagged every time you try to start something. At least it's limited to that, and it doesn't stop working on you...
I would highly recommend finding alternatives, if at all possible. Fortunately, he has no PPC SNES emulator available, so snes9x is an option that won't nag you every startup.
I'll cut myself off here before I get into more angry ranting. I just need to figure out at some point how I can improve FCEUX's performance and give it a proper GUI... if I can manage that, I'll certainly release binaries. I just have some moral problems with him profiting off others' work. (Sure, he ported them, but... the emulator cores, as far as I know, are completely others' work.)
Also, Minecraft may run poorly on a PowerPC machine. My dual 1.8 G5 struggles on it, even... yet my 2.6 Core 2 Duo PC doesn't seem to have much issue with it. Granted, there's a substantial video card difference (Radeon 9600XT 128MB vs. GeForce 9500GT 1GB), but the game doesn't look THAT visually intensive. Then again, it IS entirely coded in Java...