Include PHP in Template and call Function

[DHDesign]

so i get how to include a PHP file in my template using the Plug system, but then the vBulletin manual says that I need to put the contents of the file into a variable like $includedphp and when I want to output its contents, I just call $includedphp from the template.....BUT

my include file is just a bunch of functions and I want the template to be able to access the functions (like footers, headers, stuff generated from the DB)

so in the template i need:

<div id="footer">
<? display_footer(): ?>
</div>

...i need somehting like that work.

any thoughts? thanks!