Wanted: Web-Based Screen Saver

I've decided what I want for (quick check) Saint Zosimus' Day: a Windows-compatible screensaver that will:

  • poll a web site for an XML file containing a to-do list; and
  • display that list whenever my computer goes idle for 5 or 10 minutes.

Bonus marks if it'll run on Linux and Mac; more bonus marks if it comes with a command-line tool, a Firefox browser plugin, an HTML form interface, and a little standalone GUI for editing to-do entries. Note that running a browser in full-screen mode as a "background" doesn't count.