IF statement for EZ-Page

[milkyway]

Hi all...

I would like to know what is the IF statement for a specific EZ-Page,

example the page is at:

/index.php?main_page=page&id=1&chapter=0

I dont kow what variable control the page&id=1,

if ($current_what_to_put_here ==1) {
}

The purpose is I would like make the header changed when visitor visit that page. So I want to insert that if statement on tpl_header.php

Thanks!