1) That section has a fixed width, which makes sense to me, since if the width varies with content, you'll just have more black space on the sides. can you provide an example of a page which would benefit from an adjustable width?

2) You could add display: none; to the #navSuppWrapper rule in the stylesheet.

3) Same for the #header-navigation rule.

Get the Web Developer plugin for Firefox which will let you examine these pages and discover what you need to change. That's what I used to suggest the above. Some prefer Firebug, which does much the same thing.