Those ones won't work with a DS per say unless you have a GBA lieing around, they transfer data via the GBAs link port.
This would be more up your alley (especialy if you have a large SD card already).
http://www.gameboy-advance.net/nintendo ... dapter.htm
It was designed to run on a DS and it can play Mp3s and movies and can play NES and SNES games with an emulator not to mention NDS homebrew and NDS roms if you feel roll that way. You have to get a SD card if you don't have one but it still works out to be about the same as a normal card but with 10x the space if you get a 1 gig SD card.
If you decide to get one remember most cards use the megaBIT size and not megaBYTES. Megabits are smaller than Megabytes. In fact 1 Gigabite = 128 Megabytes.