I saw that no one mentioned getting the codejunkies MAX player for the DS. They come in 1-4GB versions. You can load MP3s, encoded videos, and homebrew games onto the DS. I have 3 full movies and several songs on my 1gb right now. Very nice quality! I can read the small subs on alot of my Naruto shows. Usually get around 30 fps and full color. Preaty awsome if you ask me. Adds a ton of life to my DS. I sold my MP3 player right after dont need it. With a bigger screen then all MP3 players ive seen. Just add a headset and im off.
I did not even mention the best thing ive found online. There is a little program that lets you play SNES games. I can not get enough of it! Its up to you to find and get it working sorry. I hope this help you enjoy your DS a little more. :D