From GameBrew - a wiki dedicated to Video Game Homebrew.
Midori is a NES Emulator for NDS.
It was participated in the NEO Summer Coding Compo 2006 (winner).
Run Midori with your NES game as parameter and it will create an NDS file for you with the game.
Control with D-Pad and A/B/X/Y.
R - Change the controls
L - Change the screen
While Megaman 1 and 2 both work with Midori, sounds are still missing.