If he's trying to open a server-side file in local notepad, if they have MSnetwork running on client machines and on the server (or server running Samba) then he could use the MIME format trick with a PHP supplied name...
First page has a form asking for the file name,
page 2 appends the network drive letter and provides a link,
clicking the link (with notepad opens a new notepad to the files specified).
The down side is that they have to be on the same internal network, the server has to be mapped to the same drive letter on all computers, and the text files would have to open in notepad on all machines.