We ask that you open your own thread so we can assist you with your problem. If volunteers such as yourself ignored your problem and instead helped everyone else in the thread you started, you wouldn't appreciate that would you?
I would like the header graphic to extend to the width of the page (as opposed to the full width of the browser window).
Can you provide a link to your site? Also if you haven't already done so you can create a child theme of Twenty Twelve and make your changes there once it's figured out what to change.
You can even download a ready to go child theme for Twenty Twelve.
Once that's setup then using a tool such as Firebug or Chrome's inspect element browser tool you may be able to confirm/play with the CSS to increase the header width.
Give this article a look to see what I'm referring to.