Doesn't seem like there's a sure fire way to downgrade without bricking your wii, but read this thread:
http://gbatemp.net/index.php?showtopic=182752Post 7.
You can try that, I guess.
Remember from now on to install BootMii...I've had it installed since it first came out. It'll help you in the future if you ever brick your wii, or run into any problems.
Edit: After looking this up some more, you can use the Indiana Pwns hack to load the latest HackMii installer to install DVDx, HBC, and BootMii.
http://hackmii.com/2009/09/silly_games/There's obviously newer posts regarding this, but that one caught my eye.