Well, mpeg2 used in dvd-video has some pretty stringent requirements, so I doubt there is much different in the video stream. Maybe your version of Pinnacle Studio needs the upgrade for the audio stream? The Handycam may be using AC3. If you are in the US, there are only three types of audio used in dvd-video, LPCM, AC3 and DTS (though DTS is the least common by far).
If you are located in a country that uses PAL standards, the audio could also be MP2.
Examine the files that won't open in Pinnacle with MediaInfo. Compare them to files that you can import successfully and see if you can find the difference.