The iPod can't play games like that. It can only play the games that came with it.
Yes, there are emulators for the Mac.
I have no idea what system Pokemon is for.
Find the emulator, find the ROM, and you're good to go.
You can find software at VersionTracker.com
As for the ROM, you'll have to find that on your own as ROMs are a legal gray area and I don't want to discuss illegal activities here.