Murray,
Durring development, it's OK to have the FE and BE in the same folder, preferably on your PC, or you can put the FE on your computer and the BE on a network file server. But when you deploy the application, every user should have their own copy of the FE of the split database, on their PC. The BE should be on a network file server, and when you link the FE to the BE, you should use the fully qualified network name:
\\ServerName\Folder\folder\appname_be.accdb
as the path. That way, when you copy the FE to each users computer, you will not have to worry about them having the wrong drive name mapped to a particular letter.