Update 8/13/2010 – there is now a plug in called Twitter Tweet Button 1.0 that can be installed and enabled via WordPress Plugins. I am still using this original method described below because for me the formatting is off with the button.
I recorded this screencast for people who don’t want to wait for a decent plugin for the Twitter Tweet Button. There are some ways to add this to the single post template manually but with my template it was a complete nightmare to do. Until a plugin is released I this might help you add the new button to your WordPress blog:
This video does provide information on how to use the append plugin to add code or text to every page/post or both: