Loopy has ported over the awesome PocketNes the Nes emulator to the Nintendo DS, heres the release news from the 2 latest versions:
(9-8-2005) Made a cart version and build tool. The format hasn't changed, so old PocketNES builders should also work. Sound and saving is still broken.
(7-8-2005) Experimenting with scaling, using tepples' alpha-Lerp technique. Use the touchscreen to adjust.