Downloading copyrighted ROMs or PKGs containing them is considered software piracy. The Better Way: PS3 Homebrew
The most stable way to play N64 games on a PS3 is through RetroArch. By installing the RetroArch PKG on a console with HEN (Homebrew Enabler) or CFW, you can run the original Mario Kart 64 ROM. mario kart 64 ps3 pkg
N64 emulation on the PS3 isn't perfect. You may experience "stuttering" audio, graphical glitches in Bowser’s Castle, or crashes during 4-player splitscreen. Downloading copyrighted ROMs or PKGs containing them is