sure you can play snes and nes on DS. get the firmware fromr4ds.com i the downloads section. get the snes emulator from snemul.com/ds. I DIDN'T RESEARCH THIS!! as for the NES emulator and instructions you'll have to get hem from somewhere else,SORRY!!
Yes, NESDS can run most games, though a few have graphical issues. just put the .NDS and the NES ROMs anywhere on the card, run NESDS, and select your ROM. Now, as far as SNES goes, SnemulDS can run many games, but graphics will never be perfect, you will need to play with the settings to play the game correctly. You'll need to put the .NDS in the root of your card and all the SNES ROMs in a folder in the root of the card labeled "SNES".
Visit http://www.engadget.com/2005/07/09/nes-and-snes-emulators-for-the-nintendo-ds/ I dont know if it will be any help. but it's all i've got.
