I've been looking around, seems like only some special models that Nintendo doesn't sell can do that, but i've also seen some stuff on youtube that made me kind of confused >_> So, anyone knows if there's a way or not?
The only way I've heard to is to just record off of an emulator. It'd be nice if Nintendo made a way to hook it up to a Wii, as that would be easier to record off of, but the touch screen complicates things unfortunately.
Geta male-to-male audio jack, connect the ends to the DS and your computer then start recording. Unless you got a hi-fi system, you can connect one line out to the DS and the line in to the computer and do the same job (the computer will recognise the sound from the sound system, which is actually the DS music). If you try that and have problems with the recording just ask.