To be able to load ROMs on a flash card, you need to know EXACTLY how every component in the card works, and how to use those to make the DS think there is a legitimate game inserted. It is very challenging (hence there are very few community made kernels - most flashcard companies don't release details of their hardware, or source for their official software, so it's very hard). You have to know a LOT about low level programming and hardware and stuff before you could even begin to think about doing something like this. Suffice to say, if you don't already possess most of the needed skills, by the time you learnt the DS would probably be long, long dead.