I enjoy the flexibility and affordable scalability osCommerce provides over any other system.
If a client came to me with this request, I'd suggest to base it off osCommerce or loaded osCommerce template which:
a, sits on a dark background (that will save you a lot of stylesheet edits and file edits)
b, possibly has the right column already removed and center portion stretched properly (that saves even more edits)
Something like this:
...then all you have to do is embed the current header (into header.php), footer (footer.php) and background image (stylesheet.css) which is fairly easy to do.