rip a movie = take a DVD and copy it to your hard drive. thats what ripping a dvd is.
burning a movie = take the video from your hard drive and burn to a disc.
now if you downloaded a AVI file, which is usually like 700MB you can use your DVD burner software and create your own dvd. which will turn that AVI into a readable ISO for the dvd player.
if you take a DVD u rent and rip it to your computer in ISO form. you can then use DVD Shrink to make it fit on a DVD disc and then burn it to a DVD for personal use whenever.
if you have a newer DVD player it will most likely play formats like DIVX, AVI, MPG, MPEG and so on. but i looked for a DVD player that could do that so yours may not. really helpful when you DL AVI TV shows like simpsons and family guy. then you can fit a whole season on a DVD and watch anyime.