Add widget in sidebar
 

How can i add a widget that spans full width of sidebar(both sidebar) on top of the sidebar?
I want to put some 125x125 ad and email subscription option on the top of the both sidebar.
Also pls suggest me what more modification could be done?

One more problem is with the left sidebar on right side. The customization is not done in left sidebar. How is it possible?
I am using 3.4.1 theme.