Charts created show up different on other computers

I created a Line Graph on the primary axis (plotting a certian number on a
specific date) and a secondary axis that has a vertical line for an event
that happeded on a specific date.
What is happening: I created the graphs and they look fabulous on my
machine, but when others view them then they are messed up. The secondary
axis does not show up the way it should be.

I have MS Office 2007 and SP1. Others have MS Office 2007 and either SP1 or
SP2.

Are there any settings that need to be updated or changed to help with this?