Moving the sidebar to the right of the header seems simple enough.
— Change #header-wrapper -- to width of #main-wrapper
— #header-wrapper -- float:left;
— Change #header-wrapper - margin:0 0 10px;
— Move <div id='sidebar-wrapper'> between <div id='header-wrapper'>'s closing </div> and <div id='content-wrapper'>
––This can easily be done with the Expand Widget Templates box unchecked
A post-change tweak to lower the sidebar a little.
—#sidebar-wrapper {
width: 220px;
margin-top: 8px;
A change like this should be worked out on a test blog before moving the changes to a live one. Add the key elements and some content, and check everything to make sure it will work as desired.