How can I set an HTML page as the desktop background?

You cannot do this with Nautilus or Compiz, no. I don't know what exactly the screenlets you are talking about are, but the general answer is no. File managers and the window manager, do not use a webkit view to draw the background and icons. This works in Windows, because the file manager and web browser, are the same thing. In Ubuntu, they aren't.

I know that this is an old question...but I just made this (BackgroundPage):

• http://ciaccodavi.de/BackgroundPage/
• or https://github.com/CiaccoDavide/BackgroundPage/tree/master/docs

I tried it on Debian and Lubuntu and it works, but I couldn't build a release for Linux...

You can try using the source code in Qt