How to place a banner between head and body

[Macsee]

I raised this question elsewhere, but I realise it may have been the wrong section.

I wish to add certain information between the head of the site and the body (just under the nav bar). It needs to be 90 pixels high and extend the whole width of the page and it needs to appear on all pages in the forum, CMS, blog.

It was going to be an SSI (server side include).

Any suggestion on which template I need to edit to insert the <include> code?