The DS can't multitask. Hell, not even the PSP can!
Until the release a game that can run music off the SD card of a DSi and someone cracks DSi mode (Don't hold your breath), It'll probably never happen.
No. You can't run ANY homebrew and you are never going to have the DS play custom music AND your game at the same time...EVER. The only chance that is possible is with a higher end card like a DSTWO...which will never have it EVER anyways.
No. You can't run ANY homebrew and you are never going to have the DS play custom music AND your game at the same time...EVER. The only chance that is possible is with a higher end card like a DSTWO...which will never have it EVER anyways.