You may download a game ROM ONLY if you are legally entitled so. By
"legally entitled" we mean:
You own the actual arcade or gamepak of a ROM you are downloading. Under the copyright
laws of the U.S., you are entitled to own a backup of any software you have paid for. Since
ROMS can't be duplicated (not without special hardware), ROM images are provided to the
public as a service.
Remember, the purpose of an emulator is to preserve games (so that they don't dissappear),
to have all your games on your PC (so that you don't tie up the family TV) and to keep a
backup of games you own in case the game (or arcade/home console) fails or have already
failed.
It's for educational purposes only (in case you are an emulator programmer).
You will NEVER sell these ROMS for profit. Most game companies don't mind the distribution
of their game's ROMS because they no longer exist, but they WILL mind if someone sells
them.
You will NOT distribute ROMS together with emulators as a package. And again, NO selling.