In order to uninstall any Google Desktop gadget you can do the following:
1. Close Google Desktop
2. Open 'My Documents' folder and locate and open 'My Google Gadgets' folder in it
3. Find the gadget you want to remove and delete it.
4. Open Google Desktop again.
(source: uninstall RSStoSpeech Google Desktop gadget - RSS To Speech Gadget | Google Groups)