do I have to use one of those official Nintendo wifi sticks?

I never did, if it is a normal DS then o to the wrench/settings. Search there. Google might be a better way to do this. And if it is a #DS go to the wrench click internet then you should find it :]

Not really. You need a broadband connection with an access point. The DS should be able to use WiFi easily then. Just make sure that your encryption is WEP.

DS/DSLite: Any game that utilizes Wi-Fi should have settings. Click a connection (there should be 3) and Search for an Access Point. It must have WEP encryption. It should work if you put in the password and connect, but if that doesn't work, try Google.

DSi/DSiXL: Same rules, BUT now it's under System Settings, regardless of game (any time you select Wi-Fi settings in a game cartridge, it refers you to the SS). Also, WPA/WPA2 connections may work (correct me if I'm wrong)

Have fun!