Right... So what do you actually wanna know?
If you're trying to store a DS rom on a original, bought DS game, forget it. They use ROM (hence the name of roms
) that means Read Only Memory. You can't write to it, you can only save in a special, rewritable area.
You can buy something like a G6 Real or something though. You have a DS cartridge just like all others with rewritable memory (accessed through PC / Mac / you get the idea).