Here is where I am running into problems though... First, there is no audio. I tried to select a different audio stream by selecting the 'info' button twice, but no luck. Still no audio.
What audio track are you ripping? If it's DTS or PCM, it won't play on the Roku. If there is a DD5.1 track, use that one.
Second, and more interestingly, it seems mplay is trying to playback both the English and the French video at the same time. During the intros and at several instances during playback, I can see that mplay is actually playing BOTH the English and the French video files. For example, when the intro credits are rolling, it plays back "Steve Martin" then it jumps and plays back "Steve Martin" again, except the font it different and there are French characters in the spelling. This happens for every seperate into credit.
Multi-angle DVDs (different languages are stored as different angles) have the video for each angle inline, so when you play it back on the Roku, you'll see exactly what you're seeing (DVD players know to skip the alternate angle, the Roku currently does not). Unfortunately, the only way to get around this right now is to rip the DVD specifying which angle to rip. I'm not sure if DVD Decryptor has that option or not. Perhaps someone who knows will chime in.