First off, your normal ISP will hardly ever have what you want to download. They usually do not carry the Binaries that most pay for servers do. You are usually limited to what your ISP has set up for you as for the download limits.
Also, if you want to find the information about Comcast, you should contact them. I don't think there are that many of us that use Comcast, so you won't find out too much info here about it.
On the other hand, like RichardJ mentioned, a payserver is what you are looking for, if you want to surpass that 2 gig limit. Depending on the payserver you can get 10 to unlimited downloads from them.
The first place I would look for information about the Usenet is
www.slyck.com - the best information available.
Hope this helps...