There is no way to do this from UI, but you could do it as follows:
Create notebook structure which you want to save as a template.
File - Save As.
At the dialog, change Save as Type = OneNote Single File Package (*.onepkg)
Page Ranges: = Current Notebook.
Click on OK.
Then, copy your saved .onepkg in to C:\Documents and Settings\[user
name]\Application Data\Microsoft\Templates
Next time when you try to create notebook, you sould see your .onepkg file
as part of notebook template list.