I have a Mac and Win95 machines and want to connect those two. If both machines have Ethernet connectivity, then you have all the things you need. Both must have a Ethernet adapter and cables connecting the two. Then, get a web server or FTP server software for either computer. Now that one of the computers can be a server, the other needs client software to access the server.
IntraNets are the application of Internet technology to a private network.
A web server just for employee use is an example. This reply assumes a network with only these two computers. Netmask of 255.255.255.0 is appropriate. This mask allows 254 computers on the same network segment. You don't want it any larger and smaller would be a hassle.