In operation, you simply take the Google Gadget's HTML code, available from Google's page, paste it into Amnesty, and voila, out pops a Vista Gadget. I tried it for several myself. It worked fine in most cases, though there were a few which were dead on arrival after conversion (parameter errors, etc.). I explain how, here.
The undeniable appeal of Vista's Gadgets points up for me the importance of the OS's eye-candy features. Many tech observers have criticized this aspect of Vista--I'm referring both to the Sidebar Gadgets and the translucent, 3-D-like Aero interface--especially since they borrow heavily from Apple's Mac OS X. Still, the more I use Vista, the more I like its look and feel. And the fact that I'm running Vista on a dual-core system with a decent graphics card means I'm effectively shielded from any drag on performance that the processing power sucked up by Aero would make apparent on a less powerful machine.
If you're interesting in building your own Gadgets (don't try this at home?) Microsoft offers a tutorial (be advised this will start a zip-file download), here.