Things You'll Need
Instructions
Locate and download an emulator for the system you wish to play. An emulator mimics the software that the console uses, emulating it. A recommended emulator for the Super Nintendo is the ZNES while a recommended emulator for the Nintendo 64 is the Project64.
Download the ROM for the prospective game, whether it be for the Super Nintendo version or the Nintendo 64 version. The ROMs contain the game files and the game's code, which is interpreted by the emulator into a game. These ROMs can be found on various sites, including The Emulator Zone and EMUParadise.
Install either emulator. Most emulators come with installers that place all the necessary files on your system.
Open either emulator and click File>Open in the upper left hand corner of the screen and then browse to the proper Mario Cart ROM. Once opened, the game will being playing within the emulator and you will be able to control it with the keyboard.