divx movies on hdtv problem need help.

Hi I have a divx compatible dvd player and I have some questions on how it plays AVI divx movies.

My AVI divx movies are all encoded in widescreen and my hdtv is also widescreen, my question is why do I have black borders on the top and bottom of my tv screen when i'm viewing my divx movies with my dvd player?.

Can I get some tips and some help please? :).