Seems like Snagit (already recommended) will do what you need, at least as far as grabbing a window, including contents of a web page that are not visible in the window frame if you so choose. It will allow you to set timers, but I'm not sure about triggers on window updates.

The application looks fairly up to date on the developer's site, but I don't have any experience running it myself. I just happened to come across it earlier in the week when looking at the company's screen casting software, Camtasia.