a simple google search could get you the entire rom collection. You could try doperoms.com if you want a selected few roms. I dont know the file type for nes roms but its not like you have more than 1 file type to choose from. Actually if you downloaded the emulator from a website, it will probably tell you what file type they are. For entire rom packages, try googling "nintendo entire rom download". I tried this with atari 2600 for the wii2600 emulator by typing "atari 2600 entire rom download" and the very first result was where I got them from. Your search could also land you with some torrents. But if there are just a handfull of games you want for nes, try doperoms.com. I just so happened to get my 3 other emulators (nes,snes, and sega genesis) with all the games for them, but then again I got them from a friend.