Thought I would post a way to combine graphs since you can only do three at a time.
This can be done on Photo Shop but I don't have it so I used GIMP.
http://www.gimp.org/downloads/

It's pretty simple to do.
Open Gimp, click on file, choose open and pick the two graphs you want to overlay. Make sure you have the rectangle tool picked. Mine always starts with the paint brush.
Select one of the graphs you want to overlay, either one will work. Click ctrl +a ( select all). Then click on ctrl + c (copy). Select the other graph click ctrl + v (paste).
Find the opacity bar, it is set on 100, change it to about 50. This will blend the two together.
Go to file, save all, name it,put it were you want it and click save. A box will pop up click export. Another one will pop up just click save. Then when you close your original graphs you don't need to save the changes.

That should do it.

Dave