how to execute php code in the vb template

[larry_wic]

I've seen the link to the functions you can run, using the < if condition> tags, etc.

i saw somethign about a plugin (i was confused on that)

I don't see / understand how you do this?
I run this little code on all my pages, as i want to track how they got to my pages
[[ yes, i use other log analyzers, other track analytic software, but i have a specific reason why i need this too]]

so I do get how i could use the if condidtion tags to do this?
i can't call the script / include it -- as i loose the refer data.
i'm pretty sure i need to run it ASAP as the visitor lands on the page.

session_start();
 if (empty($_SESSION['vREFERER'])) {
$vREFERER = $_SERVER['HTTP_REFERER']; 
session_register('vREFERER'); }

so anyone know how, where i could run this php code in the vb template?

THANKS