I did one of these (text based only) in my diablo guild. We all took the role of a character class from diablo or diablo 2 and wrote a paragraph on it and continued the story along. I thought it was kinda silly then and I still do. However if you really want to get this going, you should make yourself play the role of an N64 character and start a story. Also forget the mp3s, too many people dont know how to do that. Finally dont limit it too one sentence, just a SMALL paragraph. It really works best if you base it on one game only (preferably multiplayer with several character classes) such as we did with Diablo 2, this way you can actually follow the story of the game only incorperate yourselves into the story. Also put the story section in quote tags and any other comments outside the quote tags.
I'll have to see if I can dig up our old D2 story. It got pretty wild.