You will have to open and modify the Normal.Dotm template and make the changes there. Since Normal.Dotm is applied to all new documents, your changes should 'stick'.
To change your Word 2007 default template, follow these steps (assuming Windows 7):
- Click the Office button.
- Select Open.
- In the left pane of the Open dialog box, click "Templates".
- Ensure the file type drop-down (next to File Name box) is set to "All Word Templates".
- Double-click "Normal.dotm" (you may want to make a copy before you start editing).
- Make changes as you would to any Word document. Keep in mind, though, that any changes you make will be applied to all new documents.
- When you're done making changes to the Normal template, click Save or use CTRL+S.
If you mess it up, close word, delete/rename the normal.dotm
(usually located in C:\Users\<user name>\AppData\Roaming\Microsoft\Templates
, again assuming Windows 7), and restart Word. This should create a new, default normal.dotm
.