Well if someone is providing a nice XML file to you, it's easy to get the information. Like, for example,
one of CNN's RSS feeds. That's meant for the public to use for their own purposes and is easily done being XML.
Now that addon, if you watched the outbound http requests, you may see something like "http://username

assword@yourisp.com/accounts/data.xml", or it may open the HTML page directly and strip the contents. There's a million and one ways.
As far as a professional approach, well, there's no universal way to parse data from any given source...in a usable fashion. I have no idea how your data is formatted to start with, but it boils down to what the content-provider (your ISP in this case) provides...if that makes any sense. :freak: