This could be somewhat useful for someone who is dialed in to an ISP. In this case the ISP gives the user a temporary IP address, which only lasts the life of the session.
Windows NT4 provides an "ipconfig" command which will display the current IP address of the "local" computer, but I have yet to figure out how to do this in Windows 95. Other operating systems may have similar problems.
Since the CGI script executes on the server, it in no way relies on the operating system of the client computer. This means that this should work for any computer on the net.