This is the one thing that everybody needs to do regardless of what platform you're playing the game on.
For obvious reasons, we can't link to any downloads here. Suffice it say, you need to find a clean dump of the Super Mario RPG US release ROM file without a header. The current web-based randomizer only supports the US version. If you have a ROM with a header, there are plenty of tools available that can strip the header off.
As an optional step, you can verify that you have a correct ROM without a header by checking the MD5 checksum. There are plenty of free tools to do this, but one nice and simple one is WinMD5 Free. Open your ROM file in it, copy & paste the expected checksum value below depending on your version, and hit Verify.
NOTE: This step is OPTIONAL as the current web-based randomizer will verify the MD5 checksum is correct when the ROM is provided for you.
US checksum: d0b68d68d9efc0558242f5476d1c5b81
This step is even easier now, as the randomizer is now a web-based program available at http://randomizer.smrpgspeedruns.com. Simply go to the website and follow the instructions! This site will generate a randomized ROM for playing on emulator, or it can also pack the randomized ROM into a Virtual Console WAD file (also provided by you) for easy installation on your Wii.
If you plan to play this on a PC emulator, you're done! Load it up in your emulator of choice and have fun experiencing SMRPG like you've never seen before (bsnes/higan or snes9x are recommended). If you plan to play on Wii for more stable performance and less input lag, you can either use the Wii version of the RetroArch emulator with the Homebrew Channel, or you can install the Wii Virtual Console WAD generated by the randomizer to play on VC. The instructions to do so can be found in the next sections.