What version of Tiki are you using?
For all versions (including 1.8) the templates/tiki-top_bar.tpl template file is where to put what you want in that very top area (TikiWiki Community Workspace etc. on this site). You have to enable (put a check in the box) the Top Bar at the bottom of Admin -> Features.
In 1.9 you can put your header HTML (and configure many options in your header) in the Site Identity feature in Admin -> Site Identity (to get to that click on Admin and its one of the icons in there called Site Identity).
A third way to do it is to put your header HTML at the top of the templates/tiki.tpl__ template file.
Let me know if you need more help