To Join two network

hello
i have a compaq server and 50 client . i have a small problem . my server has an IP of 172.16.22.110 which is in 172 serise. now one of client want to put his system IP like 192.1.1.1 . once he changes his IP the clients PC is not able to Log to our Compaq Server which is loaded with Windows Server NT
4.0. so pls tell me what to do to get the clients pc to the network and tell me how to join the two different IP series into the same network .