SoftDevhave ported the Nes emulator FCE Ultra over to the Nintendo DS, heres some info:

This initial release features full compatibility that FCE features (up to 1MB images), full speed, full sound, 2 player support and is simple to run as the included program creates a DOL file of each NES image you compile.

Download Here --> http://gcemu.dcemu.co.uk/fceultragc.shtml