I had a similiar problem where I had a strong wireless signal, but could not connect to the internet.
This worked for me:
On the wireless computer: Go to Control Panel / Network and bring up the TCP/IP Properties for your Wireless card. Go to the DNS Configuration Tab and select Enable DNS. For the Host Name, I have CTED5 and I had to add the following two IP addresses:
198.6.1.1 204.177.32.2These are UUNet IP address. I am not sure if they are unique to your ISP, but I think they will get you on the net.