Hi,
1) You need a video DECODER as Windows does not supply one by default. Download and install the program K-Lite FULL:
http/www.codecguide.com/download_kl.htm
I recommend using the program that comes with it which should open by default though you can change which programs open a DVD or video file if you wish. The included program is WMPC-HC.
2) The "interactual" software is I believe just to play any extras on the DVD that only work on computers. So you don't need that for the main video. I recommend making WMPC-HC your default and if you have any extra content for Interactual just start the program manually and point to your DVD.
I had ISSUES (forget what now) with Interactual so I just removed the software. None of the content was very interesting to me anyway.