However, owning such ROMs is not that dangerous, as the game companies generally don't seem to care about private citizens possessing them. You can generally find these files fairly easily just by using Google, though you might have to sift through a few pages of junk results before you find a good ROM site.
SNES emulation is near-perfect, as is NES emulation. PS1 emulation is, generally speaking, fairly good. One thing to note with emulation of systems of the N64 and PS1's generation (and most all systems sine then) is that you need both an emulator and plug-ins. I believe there are a number of cosmetic issues with some games, but almost all PS1 games are emulatable with the right emulator plug-ins and settings.