First, this must be done with root privledges.
Open a terminal window and become root. Todo this on the terminal command line:
sudo bash
cd /
The system will then ask you for your password.
Next, lets create a directory that is to be shared.
mkdir share
Then we will enter the directory:
cd share
Create a file, in this case I used vim to add the line “This is a test file” to a file called test.txt.
vim test.txt
To make this appear on every users desktop, you need to create a symlink in the system templates directory. Note, to get into the /System/Libary/User_Template directory, it is best to /System/Library/User\ with a space on the end and hit tab to get the full directory.
cd /System/Library/User\ Template/English.lproj/Desktop/
ln -s /share/test.txt
Now, when a user logs in, the link will be on there desktop. If the user tries to edit it, they will be forced to save a local copy.