well... you can make an iso of anything, because all an iso is is an image file of the original, and it won't make any difference in size, etc. You can make image files with apps like Alcohol, dvd decrypter, clonecd, nero (makes a nero image, nrg), and many more. But I don't really see the point of making an iso of an avi or mpeg. Usually making iso's are reserved for applications which, once burned to disc, will act as installation discs for a program, i.e. games, software, etc. Making an image of an avi or mpeg wouldn't change the size, it would just be an "image" of the avi or mpeg, so why not just burn your avi or mpeg to disc as data (iso) with any burning software, no conversion involved.
A person who asks a question is a fool for five minutes, a person who doesn't is a fool forever...