Since it has to be compatible with the system on the other side of the line, only Comcast can tell you what devices to choose from and how to install them.
Kees
I currently have Comcast for Cable, Internet and Telephone service and pay a $10 a month rental fee for the modem.
Can you recommend an affordable replacement?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic