No wifi connection on DS Lite

Honestly, you might be looking at an incompatibility between the router's implementation of 802.11 and what the DS is expecting (some random extension to 802.11 or something that's confusing the DS). Can you get your ISP to give you a different model of router maybe? Or do you have another wireless access point you can use in place of that one (or behind it)?

Go to your routers page (just type the ip of the router into the address bar in your browser), it should be located in your booklet.

If your password is a WEP key, it has to be:

• At most 10 characters for 64bit encryption
• 26 characters for 128bit encryption
• Hexadecimal, ie. A-F characters or 1-9
• Key is in the first slot (DS will only function with first slot)

If still no luck, locate the MAC filtering settings, should be around security somewhere, and if it is on, add your DS Lite's MAC address to the list of approved addresses.