I'm not even sure how to describe this problem

I have a graph that displays 4 different pieces of information in a bar
chart, A-1 and A-2 both in the same year, then B-1 and B-2 information is
displayed on top of the corresponding A-1 and A-2.

See this link
http://copleyadvisors.com/pages/Extr...1stQtr2008.pdf
Page 2, Graph in top left entitled "1st Qtr CBD Vacancy".

What I'm doing now is graphing all 4 bars side by side and then moving them
so they overlap, what happens is you end up with a gap between bars in the
same year.

I've tried all different ways to do this and have not figured it out. I've
tried using two seperate graphs and having the top with a transparent
background overlay the bottom but it's impossible to get the bars to lineup
perfectly.

Thanks ahaed of time for any help.