*.avi (movie) file conversion

Since *.avi files have been coded to be smaller(lower quality), is there a program that I can get to decode them back so that they are higher quality??? Similar to decoding a *.mp3 back to *.wav format.

have a look at www.chizzil.com they have some good info on converting files..............

I was also wondering what I needed to copy my dvd's. I have looked on the net and I see dvd drives for the computer, and dvd ram. Which do I need to make backups?? (plus I like to make backups of the stuff I rent ;) )