What security type have you got set on the Home Hub? If its WPA it won't work with your DS which is really pathetic. The DS (unlike the Wii) will only work when your router is using WEP security! This means if you have other wireless devices connected to your network like a laptop, Wii or PS3 you have to keep changing the security settings on your router everytime you need to go online with your DS.
Come on Nintendo!!! Why does the Wii support WPA but your DS doesn't!!?? I stopped buying games to play online on my DS for this very reason. A simple firmware update is all thats required!