I finally convinced a friend to get a Mac and bragged about how easy everything works. He got a new iMac (loves it!) and signed up for Comcast High Speed Internet. Now there is a new MacBook in the house so I explained that all he would need is the AirPort Express in order to share the internet wirelessly for both Mac's. I went to set it up and I screwed everything up, after hours of work I not only couldn't get the Express working, I had to leave him without even ethernet internet. That's really all the info about his setup I have at the moment. So I came home to examine my own setup which is very similar: we both have the same Comcast modem (Arris TM502G) except I have an AEBS and he has a Express. So I came home to examine my setup, it has been a while since I set mine up but its been flawless wirelessly (I never used the ethernet before). So, I plugged a ethernet cable in to the AEBS and connected my MBP. Works great. So I want to try to cut out the AEBS and just connect via ethernet from my MBP to the cable modem, that's where I start getting IP address problems. When an ethernet cable is connected to the AEBS my IP address is 10.0.1.12 and works fine. When I cut out the AEBS and try to run ethernet directly from my modem to my computer my IP Address changes to 169.254.181.6 and I get an error message saying that "Ethernet has a self-assigned IP address and may not be able to connect" and sure enough, I can't. Network Diagnostics tells me to configure via DHCP and restart the modem, still no luck. As I was searching tonight I came upon some discussion about Comcast limiting MAC addresses or something? I feel really bad for leaving them with no internet. Anybody have any input?