You can modify the default user profile and add/remove/modify whatever in there, and it will get replicated in any new user account created. By default it's located in c:\users\default. When a new user account is created and it does its very first login, this folder gets copied and becomes the profile folder of the newly created account (c:\users\<account>), hence serving as a "model". Creating a file there in the desktop folder will effectively copy that file into the new user's desktop.
Moreover, this works for any other folder within the user profile (documents, appdata, favorites, whatever), not just the desktop.
