Instructions
Purchase a flashcart and a MicroSD card (up to 32 GB). Insert the MicroSD card into the USB adapter and connect it to your PC. Format your MicroSD to FAT32.
Download the firmware for this flashcart (see Resources). Unzip the two files in the .zip file and copy those two files to the SD card. Create a folder called "NDS" and copy the games and programs you want to run from the flashcart.
Remove the MicroSD from the USB adapter and insert it into the flashcart. Insert the flashcart into the DS and boot the DS. A custom menu should open to allow you to play whatever you've put in the NDS folder.