
ThumbGrid is installed to Adobe Flash CS3 (and higher) through the Adobe Extension Manager utility that comes with Flash.
To install ThumbGrid, quit Flash (if it is currently running). Double-click on the ZIP you downloaded from your Account Center profile page, then open the folder the ZIP creates. Inside will be a folder named "Extension." There will be one MXP file inside. Double click on the file to launch Adobe Extension Manager.
If you have Extension Manager installed, the application will launch and walk you through the installation process. If your computer returns an error, stating that it doesn't know what to do with the file, visit http://www.adobe.com/exchange/em_download/ to download the latest version of Extension Manager. Install Extension Manager, then retry installing the MXP file.
If Flash isn't one of the available options, quit Extension Manager. Launch Flash, and select "Manage Extensions" from the Help menu. Extension Manager should launch, recognize your installation of Flash, then allow you to install the extension.
When Extension Manager completes, you should see "ThumbGrid" listed in the Manager interface. You have successfully installed ThumbGrid, and may now quit Extension Manager.