I wish I had the money for this right now, but finally they have released a DS flash cart for the nintendo DS(not usual GBA flash), comes with a pre-loaded OS, and you can play movies, music, and back ups of DS games, as well homebrew apps among a few other things.
Nintendo DS lite $129.99 + DS X-treme 4GB $124.95 > PSP $199.99 +games+ accesories
In-DepthReview
Holy shit that is cool, I really need a DS again.
I knew they had this, but I never saw a review. It looks pretty great 
–mark
well I just bought one, and ya its works perfect :), I have tried about 15 backups all of them have worked. The only problem is that certain homebrew apps are for other flash cart systems and even then you have to set them up right, like with this one app that lets you voice chat over the ds, or an online messaging program that allows you to pictochat with others, the IRC channels work great though, needless to say, it ownzzz