You have several divs that make up the page.
In style.css find and change these two for starters.
If you have problems, get Firefox and get the webdeveloper toolbar, which allows you to edit css as you see it on the screen
It also allows you to press Ctrl + shift + F to get details of what you're looking at i.e. as you mouse over a div it's highlighted, and if you click on it you then get information about that div - all of which makes it pretty simple to track these sorts of problems down
:-)
#home #boxes {
clear: both;
margin: 0px; padding: 20px 0px 15px 0px;
width: 700px;
display: block;background-color:gray;
}
#container {
background-color:gray;
text-align: left;
margin: 0px auto;
width: 1000px;
padding: 0px 12px;
}