You do not need to install the Comcast software in order to gain access to the Internet.
Comcast's service only requires that your computer's NIC adapter be configured to utilize the TCP/IP protocol, using DHCP settings.
It would be rather hard to detail out all the methods of doing this for the various operating systems out there, so my suggestion would be to do a search on Google for your particular operating system. I have included basic searches for each operating system below, which should return a handful of appropriate results.
Please note: These results may be generic in nature, or specific to a certain network such as a university, but should provide a rough guide to configuring DHCP for your machine.
Mac OS X
*This FAQ is based on user knowledge from a volunteer core of BroadbandReports' members. This FAQ in no way constitutes official information from Comcast or any of its affiliates.