Chart/graph creation for year over year data

[deborahyr]

Can you tell me how to get year over year data comparisons to appear on a chart?

formula field for average age
formula field for average tenure
year (i.e. 2006, 2007)
Incumbent
Successor

Result in a bar chart should show:
First Bar shows Avg Age of Successor population for 2006
Second Bar shows Avg Age of Successor pop for 2007
(gap - next grouping)
First Bar shows avge Age of Incumbent population for 2006
Second Bar shows avg Age of Incumbent pop for 2007
(gap - next grouping)
same for succession tenure
same for incumbent tenure

I can easily create 4 charts to represent this data but customer would like them combined on one... Help!