Wii Speak mod
Looking here, there is a way to mod the wii speak so it is usable with a PC. I think this would make a very interesting stream, so I'll leave it as a suggestion.
What'd be cooler is finding a way to use a standard USB microphone as a Wii Speak on the Wii.
That is a really simple mod. Too bad I do not own a wii speak
Also if the chip does some amplification/modification to the sound, soldering the wire like that won't have as good quality. This is only an if as I don't have a Wii Speak to test with.