How to make content wrap sidebar

Is there a way to make page content flow back out to full width after a sidebar? For Example: I want to place advertising code for a 160x600 skyscraper to be shown on the right hand side of pages. I would like to use a sidebar widget to achieve this. But after the Ad, I would like the content of the page to expand back out to 100%, effectively ending the sidebar after the ad widget. As a bonus, I would like to hide the sidebar and ad widget depending on screen size. For example, I would only want the 160x600 ad code to show on desktops, and not wind up at the bottom of the screen on smaller devices. Any input is greatly appreciated.