About ROM injection on the Wii. Start at www.wiibrew.org
First you need to hack the firmware of the wii. Then, go here http://forums.maxconsole.net/showthread.php?t=128524
(note, follow the twilight hack method, not the modchip method). It's got a lot more info on all the possible homebrew and custom roms and stuff. Oh, and you need a copy of twilight princess and an SD card (obviously). Feel free to ask if you need more info.