AVI files in windows 2000

I have an avi files which ran fine on windows 95, when I tried to ran it on windows 2000 it has a strange behavior. It start run without any special command.
The size of the file is 2M and it has 416 frames, I have changed it and now its size is 14M and it run fine.
I don't realy understand in this format so I don't know the diffrences between the 2 files.
If you can guess what is wrong with the old file and how can I create additional file that will work good, look good and will have small size please let me know.