Hacking Noob question about Flashing hardware on NDS

[RiftReaper]

Hello, I was wondering how playing backed up DSi games off a memory card worked. I have been googling, but all i have found so far are bits and pieces. It seems to me that you can buy special memory cards that will allow you to run applications or even games on the the DSi? Is there any rom updating like with the PSP ? I read that with the 1.4 firmware you can fake headers to get games to run off of a memory card, but i don't know how you do that. I am pretty confused as to how it works. could someone please explain how you can play games or run applications off a memory card? Thanks.