Excellent start here!
If you squish the main wrapper, you'll also want to adjust the widths for the content, posts, and sidebar in this theme so the sidebar doesn't fall to the bottom. Here's how and you can adjust the widths to your liking. Note that the "#content .hentry" width and padding should add up to the "#content" width value, and the "#content" and "#sidebar" widths should add up to less than or equal to the "#wrapper" width value.
#wrapper {
width: 820px;
}
#content {
width: 607px;
}
#content .hentry {
padding-left: 107px;
width: 500px !important;
}
#sidebar {
width: 200px;
}
If you adjust the width, your header image will no longer fit. You can adjust it by replacing the image manually. Here is an example:
#custom-header-img img {
display: none;
}
#custom-header-img {
display: block;
background: url(http://tarifaris.files.wordpress.com/2012/04/banner3.png?w=820) no-repeat;
width: 820px;
height: 167px;
}
If you want to use a different image, change out the url() value and adjust the width and heigh accordingly.