After installing MacOS X Server, I had one of the most frustrating times ever. The Assistant would lock before the last part of the config process, and quitting or killing the application would do nothing, except relaunch the whole thing again.
The only way I could find to get through this cycle was to generate the file the system uses to make sure the "First Time Assistant" is needed.
If you have the same kind of problem, just type the following from a remote connection or in single user mode (commmand S at start up):
touch /var/db/.AppleSetupDoneAnd you know what the best part is? YOU ARE DONE!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020517091437875