First of all, I assume that you are converting your movies to DVD format? There are many programs that will do this, although not all of them produce high quality. Currently I am using WinAVI. I can get better quality by using TMPGenc, but it takes a lot more time and work.

I also have a DVD player that will play DivX (.avi) movies, and was pretty excited about it when I got it! You can watch movies without going to the trouble of converting them...some of the movies, however, aren't very big. Plus, I only have one of these players, and don't want to have to move it if I want to watch a movie on my other TV! I've gone back to converting movies to DVD. I have been extremely interested in reading about what type of media to use...Verbatims are usually suggested, but recently I've been reading a forum thread on afterdawn.com and the following media types are seen as the best: (not necessarily in this order, although Yuden was recommended when I said I was having problems such as you are having)

* Yuden (Taiyo)
* Maxell (Hitachi - make sure they're made in Japan)
* Verbatim

I've read that DVDRW's are not great for burning DVDs to, unless you just want to practice...

Good Luck