If your copy of the Google Desktop SDK is old, download a new one! The SDK has code samples and tools such as the Gadget Designer and Debug Console.

If you've never used the current version of Gadget Designer, follow this tutorial:

While writing gadgets, you'll need the following pages from the Google Desktop developer site:

If you have a programming question that the documentation doesn't answer, try these sites:

Finally, don't miss the Google Desktop APIs blog or these blog posts from the Inside Google Desktop blog. And try learning from or contributing to open-source desktop gadgets.