So, the IP address of your servers is hardcoded into many configuration files. What change IP does is goes through the associated files, finds the old IP in the files and replaces it with the new IP. Also, if you have changed the hostname, you'll want to include that. You may even want to consider including a hostname change, where you supply the same hostname twice. For example, if your server was xserve.home.net and had an IP of 10.0.0.5, but now you want it to still be xserve.home.net, but 192.168.1.5, you could do:
sudo changeip 10.0.0.5 192.168.1.5 xserve.home.net xserve.home.net
Of course, if this server was hosting an OD domain, make sure to include that information as well.