Main page colorbox and facebook like box In my CakePHP site when user is first entered to my site, I check for a cookie. And if I can't find the cookie, after document load from my js file, I show Facebook like box to my visitors. I show a "div" that in invisible in my page.  

I can't imagine how can I implement this in my Drupal 7 site.
Should i put the invisible div into one of my node. If so, how can I load it from main node that includes only links to inner nodes?

I would be very happy if you can write the steps or show an example of this issue.
You can use the hook_boot() to set/unset the visitor's cookie.
You can then use hook_init() to check the value of the cookie and execute some javascript to construct your div. Your javascript can be inserted in the page during hook_init() through drupal_add_js().