Trying to decide if this is worth its own thread since I don't see much from searches involving this. Threads like this worry me.
On this website you can download a channel on your wii to load applications and emulators.
Currently I have a NES, SNES, Sega Genesis, PSX, and N64 emulators installed on my Wii and it's not very hard to do. Installing the channel and the emulators isn't illegal what-so-ever, but obviously if you choose to download copywritten ROMs, that is.
Check out:
WiiBrew
You will need The Twilight Princess game disc and I use an SD card.
They have a nice FAQ if you have questions.