You want it to look like the WP home page (THIS page header)? Meaning the full width of the browser window no matter how wide the user has that? You can likely modify most theme headers to look like that using CSS and/or modifying the header.php file. If you can post a link to your site, I can give you a better idea of what CSS you need to change.
I looked at the code and it is going to be fairly tricky to change the header width because the header is contained inside the page tags and those are coded for 1000px width maximum. The header is also coded “relative” to the page — so messing with it is likely to cause major problems with the layout.
You’d probably have to recode all of the templates and a lot of CSS code to make this work right…
So I’d still stick with my earlier suggestion that you look for a theme that already has the header the way you want it.
Maybe someone else has another idea of how to do this…??