I'm pretty sure it runs most avi formats. If the videos you have are encoded using unstandard formatting then this is an issue you can have. The same applies to mp4 although this is less common. The best thing to do would be to use a converter that you know converts to the correct format for your playbook. Or make sure to download your shows/movies from an uploader that you know uses formats that will play.
You can use gspot (not X-rated) to determine the contents, both audio and video, of an avi. See if you can detect the differences in items that run and those that do not.
All you need to do though is convert the avi files into a format that'll work - if you "obtained" the videos, it shouldn't be hard finding a quality encoder - or even some of the free ones are alright.
Go .mp4 filetype with mp4 or h264 video codec and aac audio codec.