Whoa! slow down. The DS has been out for less then two weeks. A gba flashcart will probably only take advantage of the gba hadware and currently no snes emulator for gba runs mario paint... yet.
more than likely you will have to wait for some kind of flash card for the DS to come out. and the homebrew and emulation scene for the DS is just starting. give it about 6 months and im sure alot more will be known about the DS and emulation.