A complete answer would depend on what is running on your server in addition to the basic OS. For a plain-vanilla NT server, the network settings and permissions are the biggest piece. If you are running Exchange, SQL or other specialized services, such things are service account name and password become critically important.
A couple of suggestions. If you run 'winmsd.exe' from the command line and save the report, that will give you information about the services running, device drivers, etc.
The output from 'ipconfig /all' will give you network settings and you can direct that information to a text file.
And finally, you can use a utility such as acldump to create a report of the permissions and directory structure.
Also,you may want to export the registry to a text file and keep that for reference as well.
paul