Here’s how to do it:
1. Open your GMail account and click the Settings link.
2. Click the Labs link. Look for the “Add any gadget by URL” feature. Tick the Enable option and click Save Changes. Your GMail page will be reloaded.
3. Click the Settings link again and look for Gadgets.
4. Enter the URL “http://www.twittergadget.com/gadget_gmail.xml” in the textbox. Click Add and it’s done!
Your TwitterGadget is located on the left column of GMail. You may also visit the TwitterGadgets website for a more visual instruction.