Get page ID outside of The Loop

Hi, I need to get the page ID outside the loop. I’m trying to do a submenu for a few pages in wordpress, different for each one, and I need to get the current page ID, then I will write simple function in header.php, for exacly 4 pages, something like if id=5 echo – and here a code with menu for page id 5, elseif … another id and another menu …

I can’t use standard subpages menu in wordpress, cause most of that links will linked to the tekst on that page, or to outside pages.

I will be pleased for help ??