If you can run the program, select Help > Open Data Folder... then send him the EclipseLogbook.sdf file. If you can't run the software, you'll need to search his hard drive for EclipseLogbook.sdf (XP, Vista, etc. store the file in different locations).
We can't really merge data files is the only catch, so he can either keep the old .sdf file for historical purposes and keep putting new data in the new .sdf, OR he'll have to restore the old .sdf and reenter any logs completed since then.
--LarryBoy