UNIX "ln" command and Mac OS X applications

Question

I have an application hardwired to read 4 files with specific names, in a specific location. I want to move the files to the Users/Shared folder so other users can access them; however, the application must still be able to open and save them, meaning they need to stay put.
I moved the files to the Shared folder and opened read/write permissions to all users. I then used the ln command in the original location to create hard links to the files. (Symbolic links, "ln -s", are not readable at all by the application.) Finally, I set the permissions on the links to those of the rest of my files (read/write by my user account only).
The application can open the files fine, but cannot save to them at all! It returns an undocumented (but not fatal) error in a pop-up window.
"ln" is supposed to create links that are virtually indistinguishable from the original files. And I've set all permissions as they should be, to the best of my knowledge. So, why doesn't this work?
I really hope this is UNIX-solvable. My only other option is to purchase and install a file synchronization utility on all user accounts.
TIA
1.25GHz G4 Desk Lamp iMac, fully loaded   Mac OS X (10.4.3)   60GB Color iPod (4G) x 2

Answer 1

Many programs save a file by writing to a temp file and then replacing the original with the temp one instead of writing new data to the old file. That means the old file gets deleted--you'd wind up with a new file that is disassociated from the old one that still exists in the shared location. I don't know how your program behaves or if this (among many wacky save-a-file games programs may play) is relevant to the problem at hand.