Riverfold, it should be pointed out, is the maker of Wii Transfer, my favorite piece of software that I have absolutely no use for (but with a little luck I soon might!). Wii Transfer allows you to stream/play all sorts of media from your Mac onto your Wii, and it only costs $19.
You don't care about that though, you want to know how you can win a Wii! Simple: if you have a Twitter account simply send a message to @wii and you'll be entered (that's what I did, in the interest of full disclosure). If you don't have a Twitter account it is obvious that you lack whimsy in your life, but don't fret you needn't be whimsical to enter this content. Simply head on over to this website and enter your email, and an email of a friend, and you're all set.
No purchase is necessary, but if you do win the Wii I think you should get yourself a copy of Wii Transfer. It is a very cool app, after-all.