Here is a simple way to do this:
1) Start up the Macintosh with a floppy, system disk.
2) Set the startup application for the Macintosh hard disk to be the Finder.
This prevents AppleShare from starting automatically the next time the
Macintosh is started up.
3) Restart the Macintosh from the hard disk. It should boot to the Finder.
4) Use the Network CDEV to change from Built-in to EtherTalk.
5) Open the Server Folder and select the AppleShare File Server application
(click it once). Set it as the startup application using the Special menu's
Set Startup option. Be sure you don't select MultiFinder in this step,
because the AppleShare File Server software is not MultiFinder-compatible.
6) Restart the Macintosh, and it should boot to the AppleShare File Server
software, now using EtherTalk instead of LocalTalk.
Note that with EtherTalk version 1.2 and later, you can switch network
connections without going through this process. The CDEV alerts you that
network services will be disconnected and unavailable until restarting. A
cancel option is available.