there is a emulator for nes but i dont know if it works on diamond. its called pocketNES, google it. i had it on my kaiser with a lot of roms like mk2,streetfighter etc. but i dont use it anymore and havnt tryd it on my diamond. but everthing you need is on the net.
But wait , i found it on my pc. heres the cab.
I also have the cab of the superNES emulator. here you go
I posted 2 zips with supermario3 and tekken2 in it for people to test, just unzip and put the .nes file on your internal storage,program will find it.
Also you might have trouble with missing hardkeys. I have it on my old device and it only works fine with the hardkeys. Touchscreen always recognized only one touch at a time (which is of course not enough for Super Mario...) - but may that works now