I long ago deleted the stock RSS gadget in Vista since I wasn't using it. Just the other day I decided I wanted it back for a special application. All is not lost. Those gadgets are stored in Program Files, presumably just to prevent people like me from doing permanent damage. I found the following step in the online help articles to recover the gadget.
Note: If you uninstall gadgets that came with Windows, you can restore them to the Gadget Gallery by following these steps:
a. Open Windows Sidebar properties by clicking the Start button , clicking Control Panel, clicking Appearance and Personalization, and then clicking Windows Sidebar Properties.
b. Click Restore gadgets installed with Windows.