Motorola SBG6580 Gateway acting as router/wireless access point

Comcast recently installed their triple play into my home and its great so far. The only problem is that I have to provide my own router, which I DO have, but the speeds are very timid compared to the Motorola SBG6580 Gateway I already owned. The modem they provided me with is an ARRIS telephony modem and supposedly I HAVE to have a coaxial and phone line connected to it or else the phone/internet will not work. I tried moving the telephony modem downstairs where it can just do the job as a modem and telephone bridge thing, but it won't connect that way. I want to set up my gateway as my main source of internet. Please help! Right now I have the Coaxial connected to the modem, and a cat6 wire running from that modem to the gateway, but unfortunately the gateway will not wireless distribute the internet (though the gateway IS connected to my desktop)

This should be a very straight forward setup. Are you sure the modem is connected to the router, LAN to WAN, respectively?

[modem](lan)<-- wire -->(wan)[router]

P.S. Just realized something, are you trying to use your old Motorola SBG6580 Gateway as your router? Because if you are that won't work. The SBG6580 is actually a combo modem+router, thus it doesn't expose a WAN port. It only has switched ports and a coaxial port. In effect, the WAN port that would traditionally be exposed by the router when the modem and router were separate components, is now internalized. Makes for a small footprint and convenient setup, however it also means it can't be reused in situations like these when you *must* have an exposed WAN port.

So unless the SBG6580 has an option where you can somehow disable its modem and perhaps remap a LAN port to a WAN port (doesn't seem likely, but I throw it out as a very remote possibility), that device can't be used. You need a new router (as in standalone router).