These boxes are from skin1/customer/home.tpl
They have classes VertMenuLeftColumn and VertMenuRightColumn.
To center your page you should find the line
HTML Code:
{include file="rectangle_top.tpl"}
and change it (in my example to 750px)
HTML Code:
{include file="rectangle_top.tpl" width="750"}
add in your skin1.css
HTML Code:
BODY{
text-align: center;
}
TD.Container{
margin: 0px auto;
text-align:left;
}