Don't think so. It'll pickup the analog signals that are in your comcast service, but it cannot decode the QAM signal used to encode the SD and HD cable channels.
Check thegreenbutton.com; there is an ethernet-based tuner box in the works that can decode the HD QAM signals. Drivers are in beta, and setup is an involved process, but it may get to a point of prime-time readiness soon.
The only QAM tuner that AMD/ATi offers will be going only to large Mfr's e.g. Dell, HP, etc.
If you see anything to the contrary, please post as I'm interested in this stuff.