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You will most likely need to update your codecs for the version of windows that you are using. For Windows Vista there is a Vista Codec Pack that contains many of the common ones. You may also want to download xVid and DivX codec packs as well. Depending on the file extensions and decryption/rip method will depend on the file you will use. Files with the extension ".avi" are most commonly either using a divx/xvid codec. If the files are ".iso" then you will need to get a program that creates a virtual cd-rom/dvd-rom drive, as these are actual images of the disk that you decrypted. If there is a folder for audio and a folder for video files, then you will open the first sequential ".vob" in the video directory. Assuming that you have the right codecs for the specified files, these solutions should work for the applicable file type. If you have a MAC, good luck. :p I only do PCs.
Did any of that work? What file types are you trying to play? I am assuming the ".VOB" with audio and video folders. I just recently reformatted my computer, so I now need to do the same. Please let me know if you have trouble and I will try to figure out which codecs you are missing.
Another good program for ripping dvds that I used in the past is DVD Fab Platinum. Not sure how it stacks up anymore.
I know stuff.