Believe it or not, some folks don't actually have a wireless network set up in their household. No Wi-Fi network can be a real buzzkill for DS owners. Luckily the folks at Mac OS X Hints have written up a semi-complicated method to get a little Wi-Fi connection using an AirPort card. Basically you need a computer that is connect directly to the internet via Ethernet preferably and a AirPort card ready for some Ad Hoc'ing.
The OS X Hints guys managed to explain this process in four steps. I don't know, I am still kind of weary about that. I tried to set up Ad-Hoc between a laptop and my PSP one time. Two hours later I was still internet-less on the PSP and my brain had melted into a puddle of goo. (Note that I was trying to do this on Windows.) Oh well. Good luck and happy DS'ing—if you can get it to work.