Stockpile of emulation and rom links here...tons of useless crap, too...but hey, emulators and roms are essentially illegal, so take the good with the bad.
As I know it, only the ROM is illegal to have - the emulation will enable a user to take a ROM image off their original media and provide a backup of their own data (e.g. their purchased game). Also illegal are BIOS images, like from the PSX and Neo-Geo.

Like I said, this is my understanding - is this not correct?