Active Clients Computer Summary Report

In ITMS 7.1, there's a "Computer Summary" report under Reports->Discovery and Inventory->Inventory->Cross-platform->Operating System.  I'd like to modify it to include only clients who've checked in with the server within the last 30 days.  For my old Altiris 6 server, I set my data purging to 30 days so reports would always have fairly current info.  Yah...I know I could do the same with 7.1 although figured maybe I should do some research on cloning/modifying the existing Computer Summary report in case someone wants historic inventory data in the future.