I don't know how to create widgets for the desktop, but I know that it's fairly easy to get started with a web browser using the QtWebKit module.
http://doc.qt.nokia.com/4.6/qtwebkit.html
Combining this with the Home Screen Widget example should probably give someone a push in the right direction:
http://labs.trolltech.com/blogs/2010...creen-widgets/

The idea sounds pretty decent, but I'm also guessing this will quickly become the most battery consuming widget we have yet seen!