I'm working on a line graph on a dashboard. Some of the lines overlap because the data is the same. For example, the number of units is the same across multiple months for both lines/years. Thus, the lines follow the exact same path. The user can select only the 2007 data, not 2006. Is there any way around this? Thanks!

use a bi-polar line graph
in the first you show 2006 and in the second 2007.

or an combined bar and line graph.
bars for 2006, line for 2007