First, set your SETI prefs in a working install on another Mac. Set the client to start right away and blank after one minute. Then kill SETI.
Now copy some files over to the 7100. Copy SETI@home data and SETI@home Preferences from System Folder/Application Support. Also copy SETI@home from System Folder/Control Panels. Put the copies in the corresponding positions on the 7100.
If you can launch SETI on the 7100, go ahead. Otherwise, reboot the 7100. A reboot is required for the screen saver to be enabled -- kinda nice in case the app quits for some reason.
Notes: If you are running an OS version before OS 9, the SETI Data and Preferences files will be in System Folder/Preferences instead of Application Support. Also, launching the app on a headless box will leave the window open and graphics running -- use the screen saver.