Ds lite to the internet?

Wait, so you are asking how to connect to WiFi to trade with your sister, correct? If so, then you need a router. If you already have one, power on Pokemon White and when you are on the screen where you choose your save file, click down until you see something labeled as 'internet settings' or something along those lines. Click on it. You will have the option to search for an access point. Do so. After it finds your router, click it and type in your WEP key to connect. B&W can use WPA, but the DSLite cannot, so if your router is using WPA as it's security you'll need to change it to WEP. After typing in your WEP key it will try to connect. If it works then you are all set. Start up Pokemon White and check your key items to see if you have the Pal Pad. If so, go to any Pokemon Center and talk to the middle lady at the top floor. She will connect you and you will have your Friend Code set in your Pal Pad. Exchange this code with your sister and you guys can trade when in the WiFi room, which is accessed by talking to the middle lady. This can be a bit confusing, so if you need any further help, message me through my profile and i'll be glad to help.