From the OneNote help:
Customize a page template
In Microsoft Office OneNote 2007, you can use templates to apply a uniform
page layout and design for the pages in your notebook. Page templates can
enhance the appearance of your notes through consistent use of color,
background images, and text formatting.
If you do not want to create an entirely new template yourself, you can
easily change the contents and appearance of an existing template and then
save it as a custom template.
1.. On the Format menu, click Templates.
2.. In the Templates task pane, Under Add a page, click a category, and
then click the name of the template you want to modify.
3.. On the File menu, click Page Setup, and then in the Page Setup task
pane, change any options you want.
4.. Change any content on the page so that it is the way it should appear
whenever new pages are created based on your modified template. Likewise,
delete any existing template content that you do not want to keep.
5.. At the bottom of the Page Setup task pane, click Save current page as
template.
6.. In the Save As Template dialog box, type a name the Template Name box.
7.. To apply this template to every new page that you add to the current
section in your notebook, select the Set as default template for new pages
in the current section check box.
8.. Click Save.