I'd like to have my side bar on the right to be larger on top (which would allow for a square ad) and then be a double right sidebar below it similar to on http://mashable.com/ is this possible?

Thanks.

the sidebar is the same side through out. what they have there is a sidebar that is broken up into different areas, some of the areas are full width and some are half width.

take a look at http://forum.bytesforall.com/showthread.php?t=5419 for some ideas

You can use widget areas to emulate that look. You just use a text widget that can read php code and put a two celled widget area in it. See ATO>Add New Widget Areas. Also search this forum for widget areas in the sidebar as that was covered pretty well in some past posts.