How can I do something like this?

I don’t know, but why would you?

It appears that the DS’s is simply running a homebrew GBA game, and the “hacker” (and I use that term loosely) has a video input in it.

In English:
Nothing on the DS is modded, its just a GBA “game”, bought here

If you want to follow up on this, PM me and I’ll make you a diagram on how to hook things up, even though you could probably figure it out.

Why on earth would you want that?

compared to those $300—$500 dollar attachment screens that only work with one console? Why wouldn’t I want this?

my wii works with my tv…and 52” is better than a DS screen.

Well what If I don’t have a 52” tv on me? I just want to try it for fun and experimental purposes! Is there something wrong with that?

not anymore than something being wrong with asking why you want to hook a
Wii to a DS, but apparently that upset you. Have fun.

Your DS is the biggest display you’ve got?

no. I just want to try it for fun.

oh… ok then, have fun.

crap if i know