hey man i'm having the same problem. my DSi can find my wireless connection but can never connect to it. i successfully have my PSP, Wii, and PS3 on my wireless signal already so i know it's not my signal.

the weird thing is that when i test the internet connection on my DSi it kicks my PSP and laptop off my network. i have to unplug my router and modem in order to get back online with the laptop and PSP.

it's frustrating since the WiFi was a major selling point for me in purchasing the DSi.