Image Alignment and The Header
Images are fully supported using the floatLeft and floatRight classes. Just apply one of them to the image you want to position. Images that have link tags around them will also have a nifty rollover effect, as long as you're using a standards complients browser. If you're not, well then no rollover effect for you.
The site header images are two slices and a repeated background. Using the same approach, and a little bit of photoshop, you should be able to easily replace them. However, since they were created by Pat Heard, you're welcome to use them in any projects you might like.
The Footer
A variation on the footerStickAlt technique is used to force the site footer to the bottom of the page if there isn't enough content to push it down. This means your template will always look tidy and you won't have to worry about a lonely footer, hanging out halfway up your page.
Readability using Maximum Width
To improve readability of this template (since it is fluid), the width is capped at 1000 pixels. This seems like a pretty reasonable thing to do and that's why CSS has thoughtfully included the max-width property. Unfortunately, IE decided it didn't need no stinkin' max-width, so a CSS expression was needed.
A CSS expression is like a snippet of javascript code that runs in your style sheet. It's invalid CSS, but only IE pays any attention to it.
If you're concerned about having valid CSS, take out the expression. It won't ruin the template in IE, it just means that the content will expand to 100% of the screen width. All other browsers will behave.