Although I don't have an answer for you I can say that I have Rogers High Speed with that exact modem and an Intel iMac. Everything works perfectly, although I am connected through a router. Give Rogers a call... sometimes you get a support person who knows about Macs, sometimes not.
24" 2.8Ghz iMac Alu, 3Gb RAM
180G LaCie backup
Ti Powerbook - still humm'n
I'm not sure if Rogers still does this or not, but I had a similar problem many years ago when I upgraded my desktop (a PC at the time). Also at that time I was not using a router.
Rogers had associated my connection to the modem with the MAC address of the device connected to it. When I plugged the new machine into the modem, I had to call Rogers to flush the MAC address so the new one would be picked up and I could then use my connection.
Again, I'm not sure if this will help or not, but it's worth a call to tech support about.
When we moved into our new house a couple of months ago - and had a couple of simple questions about setting up my wireless router correctly - I was told by the TechRep that Rogers will NOT provide "help" past their modem - reason: they have no record of what the customer has installed. He suggested I call the router mfg to ask my questions. (a reasonable explanation, I suppose)
Obviously he has a router otherwise how could his PC, Q.silver and other tenets get Internet connection.
From what I understand, he's been connecting them manually, and using Internet Sharing to share the net with his tenants... or at least trying to. A router would solve all of these issues, as well as the MAC reset suggested before.