John,

I had to do something very similar recently.

Have a look at Jon Peltier's excellent page and the links from it:

http://peltiertech.com/Excel/ChartsHowTo/ClusterStack.html

Dave

ClusterStack is overkill for this.

All you need to do is chart the first two series as a stacked bar, and then
move the target to the secondary axis. Once it is there you can choose a
different chart type of you want to, although you could leave it as a stacked
bar with only one bar in its stack.
If you have Excel 2000/2003 you plot all three, then right click the Target,
goto Format Data Series, choose the Axis tab and select "Secondary Axis".
In 2007, the principle is the same, but the choice of Axis is under the
"Series Options" section
In order that the Target does not obscure the other series, you should make
the Gap Width bigger for that series, resulting in narrower bars. How much
narrower is down to you.

A neat way to show these is to actually have a fourth series containing very
small values (eg 0.001). Stack this series on top of Target against the
secondary axis. Make the Target series invisible with no fill and no border,
and then the extra fourth series will appear as a nice floating horizontal
line across the income figures at the level of the target. This is easier to
get right in Excel 2007 - older versions can make these disappear if they
coincide with other elements such as the top of another bar.
You should also tidy up to remove the secondary axis to avoid too much
visual clutter.