How to Add the Latest Tweet Box on Tumblrby David Nield
Tumblr enables you to customize most aspects of your blog. You can switch between themes, choose a title and description, set your avatar and add custom CSS code to tweak your theme's appearance. You can also add widgets and your own HTML to a theme through the customization screen, including the official Twitter widget. Depending on the theme you're currently using, some tweaking of its code may be required to make the tweet box appear in a way that you're happy with.
Log in to Twitter, click on the gray gear icon on the toolbar and choose "Settings" from the drop-down menu.
Select "Widgets" from the list of links and then choose "Create New."
Under the User timeline tab configure the widget as required in terms of its height, color and theme. Click "Create Widget."
Press "Ctrl+C" (or "Command+C" on a Mac) to copy the selected widget code to the system clipboard.
Log in to Tumblr, then click on the gear icon above the dashboard to access your account settings.
Select the name of the blog you want to work with. Select "Customize" by the Theme heading.
Click inside the Description box and press "Ctrl+V" (or "Command+V" on a Mac) to paste in the Twitter widget code.
Select "Save" to confirm your changes and then "Exit" to return to the Tumblr dashboard.