Hey, last night I was massively thrilled because I managed to get a DOS emulator working on a flashcart for my Nintendo DS. I'd love to add some of my GOG downloads to the cart and be the coolest kid on the block playing his legally acquired DOS games on his DS like some kind of modern day James dean only instead of a cocktail stick in his mouth as his visual trademark I'd have a DS in my hands at all time and instead of being cool and famous I'd be a guy who has legally acquired DOS games on his DS.

But when I extracted dosbox-0.74 I couldn't find the actual game files anywhere in the archive. Does anyone know where they're hidden away. Is there something else I need to extract?

What archive are you talking about, do you mean a GOG installer or the copy of DOSBox you downloaded from the DOSBox site?
Also be warned, few games will be playable on a DS for two reasons:

1. the DS isn't all that powerful, the emulator will be really slow

2. the DS's screen is only 256x192. The lowest common resolution for DOS games is 320x200

The flashcart has a built in processor that helps things along, the games don't run perfectly but they work.

It's the GOG install file, they all come with a copy of dosbox and an archive called dosbox-0.74.tar.gz I know the files must be in there somewhere but I don't know where to look

Uhm no, I'm pretty sure that's just GOG sloppiness.
In most cases you'll want everything but the DOSBox directory since that contains the DOS emulator which you don't need in this case.

Oh and a lot of GOG games also have renamed ISO files in the directory, called <something>.GOG or <something>.INST for example. You can find out in the DOSBox .conf file, at the bottom in the autoexec part (I think) it will have a line about mounting that file.

Try the inno setup unpacker: http://innounp.sourceforge.net/

And then something along the lines:
innounp -x setup_kings_quest_1_2_3.exe

That archive is DOSBox, not the game. The easiest thing to do would be install the game on Windows, and then (as Smannesman suggests) copy the entire game directory minus the DOSBox directory.

I'm afraid I don't know much about the file structure of the games within the installers so I can't suggest where to look if you're rooting around inside the installer.

I've heard of those flashcarts with co-processors, but I still think the DS's small amount of RAM and not especially powerful CPUs will be too much of a bottle neck to allow most games to be enjoyable. Plus there's the whole screen resolution thing...

What game are you trying to unpack by the way?

Another useful program for you would be Universal Extractor, which also works well at unpacking the GOG installers: http://legroom.net/software/uniextract/