If you have a computer set up already that you want to have broadband access, Comcast should run a split to that area. If you want to access via wirreless, the router must be able to do it. Otherwise, you might need something like a Wireless Access Point to plug into their router.
Without all the details about what you have... it's hard to be more specific.
I have a D-Link WBR-1310 wireless router.