I am not sure what exactly is involved in this comparison, but you cannot have two found sets in the same window. So one way to do this could be to open a new window.
Another option is to use two relationships, with a pair of start/end dates for each.
Just to throw in another possibility, you might be able to use sub summary layout parts to separate your two groups of found records into two subgroups on the same list view layout. If you have FMP 10, this will be pretty nice as you can see these parts in browse mode where you would have to preview or print the layout to see them in earlier versions.
As comment said, describe in more detail so we can help in more detail. (If comment's excellent suggestions turn out to be the way to go, I'll bow out and let you two go at it.)
The new window was a quick and easy solution. I am going to try the relationships with start/end dates this weekend.
This is what I am doing. I use FM to keep track of my cycling workouts; date of rides, miles ridden, avg. MPH, time ridden, ect. I have a calculation field set up to total the miles ridden. I like to compare months from different years. What I was wanting to see or set up was a find that would allow me to see the information collected from the month of April 2008 and compare it to the information being collected for the month of April 2009.
I like to compare months from different years.
If each of the compared groups will ALWAYS have some distinguishing attribute (such as month or year), you could indeed find them both and produce a summary report.
I've created a 5 year comparison report for some of my solutions. Each Row is a different month and each column is a different year. Just to clarify your request, how close does that come to what you want?