1. Go to: http://twitter.com/about/resources/widgets/widget_profile
Fill out your username and preferences and then grab your HTML code.
2. Login to your site as an admin.
3. Go to: Settings > Template (tab) > Manage Side Column - and choose the side column you would like to add your Twitter widget (Default Side Column normally).
4. Click "Make a new section".
5. Add a "HTML Section".
6. Click the HTML button and paste your HTML code you grabbed earlier.
7. Click Update.
You may now rearrange your Twitter feed where you like in the side column area.