Just a simple "make this site widescreen" and making things how I would like them.
Made the header, yellow bars, content 100%
Made the Navbar a fixed position at the top of the browser window, and highest z-index. This'll mean your buttons stay at the top of the screen, easily accessible. Stays even if you scroll.

Only tested on Firefox + Chrome.

Changelog
9 September 2014 - Corrected invalid code as per Admin instructions. Adjusted for new Openclipart Site coding.
3 May 2011 - Position Fixed the search bar. Z-indexed search bar to top layer. Always available now.
2 May 2011 - Made the nav bar a little bit better.
Pulled in the login / register buttons into hover nav bar so that your tools are always in reach.
Moved Launchpad buttons to the left
Centered the sidebox titles
Adjusted header spacing to suit new navbar position
Corrected footer width to 100%

To do :
+Columns fix for My Profile when user is logged in
+Keep clipart, close, and multiple columns self-adjusting
+Pullout of flow and make-drop-down of stats, to allow for clipart to flow in columns as above on numerous pages. e.g.artists page.