Can your run a looking glass script at home, and see what the BGP route is to a given IP via your cable/dsl provider?
You generally are not given access to your upstream ISP's routing table.
You can infer how they route with traceroute for a given destination IP. (keep in mind that this can change over time)
You could also write a script to login to other external looking glass systems to see how a particular route is being announced to the outside world. That might give you some insight too.
Route Views is one well known one. http://www.routeviews.org/