When you first open FW office and come to the Project Selection Window, highlight first project name. Click the Change Project Info button. Displayed will show the matching 0000000#.prj Directory. You can also find this number, by going to the Help - About FW Office. Right click the version number will be the Directroy ID number as well.
You may also want to continue making individual project backup files and save to the C:\Farmproj|Backup Folder. Add this folder to your system backup process.