In Windows, just use the following synthax in the php command "copy":
You need permissions to copy files (check the configuration of the webserver you're using, the user who's running the webserver must be included with r/w permissions).
If you haven't permissions, run a
system("net use drive1: \\server_source\path password /USER:email@example.com");
system("net use drive2: \\server_dest\path password /USER:firstname.lastname@example.org");
You must know which drive letter from Z: down to E: are available on your server.