Many Wii users have complained about the inability to playback DVD movies on their Nintendo Wii. Nintendo has several times responded unvillingly to do something about this issue and recently stated that they have no intention of making the Wii DVD compatible. However, talented homebrew coders have taken action in their own hands, releasing a solution that will make this possible.

Through installing a small hidden channel on your Wii called Homebrew Channel and using Mplayer, you should finally be able to enjoy DVD playback with your Wii. Media playback from SD cards is also an included feature in the software (still in experimental stage for now).

"As you all know, I’ve been working on libdi (or the DVD Access library) for a while now. We had some problems getting it out to release because of the difficulties we encountered while writing the second part of this topic. The DVDX installer instead will install a small, hidden, channel on your Wii that allows you to read DVDs on an unmodified system. It is not an installer for a patched IOS. You may however need one, depending on your system."
source: HackMe blog