I personally do not like it, it makes my every atom shreek to look at brown and pink, and azurre mixed on any kind of layout that's not a cupcake.
if you really want to make something that ugly...
modify MY_TEMPLATE/common/tpl_header.php to get the file layout you need in the top
then use CSS to change the background color of the page, create the menu on the top and make nice mouse hovers on it...
position the logo, if you did not already do so with the image.
also you want to give eveything inside the cart some nice spacing, margins are the crucial part of a clean desing.
the "intended" empty space is a must for a professional design, and it's a concept that is not tought of in classes usually.
my personal raccomandation is to give the #mainWrapper a min-width:750, and width:some%, so that the design is liquid and expands to fit bigger screens, while never going under 750px of with -- on modern browsers.
to achive the same result on IE5, js is your friend...
really i make at least 4 or 5 of these a day -- altough never mix brown pink and azzure togather... so I probably lost you by now... but my raccomandation is to start with something in photoshop, and get it to be something you like, then pass to the "replication" process of making it actually happen with HTML, CSS, and JS.