ExpressInvoice-Mac stores its files in: Macintosh HD/Users/<the user>/Library/Application Support/ExpressInvoice/Shared. (Macintosh HD/User/<the user> is also the folder that appears in Finder as the user name.) -- The Library folder is hidden - to make it visible, open the user folder in finder, then View->Show View Options, and select Show Library Folder. If you can find where the old files are located (the data is a bunch of folders containing .dat files), merely copying them into the current EI save folder should do the trick.