Addressing your inquiries in order:
1) Sorry, we do not have a version of our script source available for public release or examination. If you're just curious about the HTML/CSS/DOM structure of the cart overlay itself, you can open an Add to Cart button's href= URL in its own tab and then view source, or view the cart overlay inside your page and use the View Source Chart extension for Firefox to examine how our cart code has been dynamically added to the end of your page's original source.
2) That part of our View Cart code is intended to suppress the cart overlay from appearing immediately upon page load in some circumstances. It should appear in your page source before the line calling our box.js script; if it appears after the box.js line, it would suppress the cart overlay from appearing at all. If the cart overlay doesn't appear in your page as soon as the page loads, you can probably do without the function EJEJC_lc(th), but it doesn't harm anything either, so you might as well keep it just in case it becomes relevant at some later point in time.