Background image in the home page sidebar area?

How do I place a background image in the sidebar area of the home page. The image I currently have on site is something I put together to replace the twitter.png I would also like to remove the other sidebar image, the grey framing.

Also on the site home page I have a slideshow that I'm using via a plugin, however try as I may in the editor, I can't get it to center on the content section. Any suggestions?