Comcast modem locks up/kicks off internet when Vista wireless connects to existing connection

Business and home account doing the same thing: Whenever someone goes to get on the wireless network connected to Comcast with a Vista machine, the Comcast modem locks up (light goes steady and no one can connect). At work we have Embarq business internet that comes free with our phone system but we don't use it and are not connected to it in our comunication closet unless the cable goes out in our area (lots of storms so this can happen) and I go plug into it. Ran a test, though, using our same wireless router (Netgear) and when it is connected to Embarq, this lock-up issue does not happen. The lockup issue also does not happen when connected to Comcast but someone with a Mac tries to connect wirelessly. It does not happen when everyone uses a network cable to connect. This is an issue specific to Comcast, with Vista, connecting wirelessly. To "fix" it, we have to unplug the Comcast modem, and router and then plug them back in (reboot). This can be a pain for all those in the office (not as much of one at home since we have gotten used to it by now) every time a consultant comes in and logs in wirelessly or someone browses to our wireless network trying to use it (even if they can't connect becase they don't know the password).

I have a feeling that Comcast is going to blame Vista and Microsoft would blame Comcast but really, Comcast should be looking at the issue since Vista, for better or for worse, is one of the most prevalent O/S and it works with other companies' services.

Please help.