Apocalyptic980c created a tutorial outlining how to legally run homebrew and emulators on your nintendo wii. It requires an sd card
, and some special formatting / homebrew software to get everything up and running. You do not have to modify your wii console in any way, and emulators include Snes, Genesis, GameBoy Advance, Gameboy Colour, PC Engine and Nes and also a port of Doom.