Jet: Narrowcolumn and Widecolumn are never both used on the same page. Narrow is for archive and index pages (and the main page); wide is for individual entries.
1. Find <b>#sidebar</b> in the CSS file (it’s near the bottom).
2. Increase the narrowcolumn width by some amount (say, 50px), and decrease the sidebar’s <i>margin-left</i> by the same amount.
Magnumgrp1: the gray image is for the very edges of the page; the sidebar background color is built into the kubrickbg.jpg file.
There’s a quick fix if you want to get rid of the gray color and make the sidebar and main content area the same shade (white, that is). (Once you’ve done that, you’ll be able to move the sidebar wherever you want using css).
Find kubrickbgwide.jpg file, download it, rename it kubrickbg.jpg, and upload it (overwriting the old file).
You can see this in action on my (slightly unfinished) site.