The browser is on a cartridge just like a game. It also comes with an additional RAM cart, so you can actually load websites. You can't actually download stuff permanently as there's no storage beyond the bit of RAM you get with it.
Here's the wiki:
http://en.wikipedia.org/wiki/Nintendo_DS_Browser
Like I said, I think it was worth it, but it's not without its problems. It's slow. No video, audio or Flash. And everytime you want to connect to a connection you haven't used before, you have to configure a connection which can take a minute or two. Annoying if you're on the go.
Re: You probably already figured this out already, but...
Here's the wiki:
http://en.wikipedia.org/wiki/Nintendo_DS_Browser
Like I said, I think it was worth it, but it's not without its problems. It's slow. No video, audio or Flash. And everytime you want to connect to a connection you haven't used before, you have to configure a connection which can take a minute or two. Annoying if you're on the go.