Since most AVI files are compressed with different codec, it is common that your computer can play some AVIs without any additional software needed and meanwhile refuses to play some AVIs.
This is simply due the fact that those AVIs have been compressed using a different codec and your computer has a codec installed already for the ones that work. Although still supported in Windows and suitable for certain formats like DV, it's not a good general purpose container, and even Microsoft uses other containers for their own video formats.

About MPEG
MPEG-1- Audio and video compression format coding of moving pictures and associated audio for digital storage media at up to about 1.5 Mbit/s. MPEG-1 is the video format that has had some extremely popular spin-offs and sideproducts, most notably MP3 and VideoCD.
MPEG-2- MPEG-2 is not a successor for MPEG-1, but an addition instead -- both of these formats have their own purposes in life; MPEG-1 is meant for medium-bandwidth usage and MPEG-2 is meant for high-bandwidth/broadband usage. Most commonly MPEG-2 is used in digital TVs, DVD-Videos and in SVCDs. Some Blu-ray films have MPEG-2 transfers but not many as there are better lossy compression formats such as VC-1 or MPEG-4 AVC.
MPEG-4- MPEG-4 is one of the latest (audio and video) compression method standardized by MPEG group, designed specially for low-bandwidth (less than 1.5MBit/sec bitrate) video/audio encoding purposes. Probably the best-known MPEG-4 video encoders are called DivX and XviD, which both are nowadays fully standard-compliant MPEG-4 encoders.
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