In July 2008, the ESRI Prototype Lab published an extension to ArcMap that added support for MetaCarta's GeoTagger OnDemand service.  This extension is now available as a custom task for ArcGIS Explorer.  The task is available as a free download (including source code) from ArcScripts.

Before you can use GeoTagger for ArcGIS Explorer you must create a MetaCarta account and signup to use MetaCarta web services.

1. Create a MetaCarta Account
   Visit http://accounts.metacarta.com,
   Enter your email address and pick a password,
   Enter your name, address and telephone number (optional),
   Click the Create Account button.
2. Sign-up to use MetaCarta's Web Services
   Visit http://accounts.metacarta.com/account,
   Enter your username (email address) and password as entered above,
   Click the link “agree to the terms and services” link,
   Read the license agreement.
   If you agree check “I have read and agree the...” and click the Submit button.

The source code is available post-install.  The default location of the source code is C:\Program Files\GeoTagger for ArcGIS Explorer\SOURCE.  The task will be automatically be install for the current user in C:\Documents and Settings\<profile name>\Application Data\ESRI\ArcGIS Explorer\Tasks (in XP) or C:\Users\<profile name>\AppData\Roaming\ESRI\ArcGIS Explorer\Tasks (in Vista).