As a work around the best suggestion I can make is to go right to the networks own website and try and watch from there.
Make sure that you're using the latest version of the Flash player, you can check that here: http://www.adobe.com/software/flash/about/
You didn't mention which browser or operating system you're using, if you happen to be using FireFox there's an extension called Live HTTP headers which you can use to capture what's going on in the browser when you're getting that buffering message. By providing the information and private messaging the Comcast people to look at it, chances are that you may get the problem fixed.
- Norm