How to make an avi movie file smaller?

i have a lot of downloaded movies, that are in avi file format, and i need to make the file smaller so it'll fit on a dvd when i burn it. i've tried making a data dvd, which has worked before, but now i can't get them to play on my dvd player. any suggestions? i'm using the free trial of Nero 10 multimedia. and my dvd player is a samsung ht-x50. i've tried using dvd shrink and easy dvd shrink but i keep getting errors when i try to shorten them.