I figured out how to keep AFP Volumes mounted always!!! It's actually quite simple.
Here's how to make the change:
Just go to your NetInfo Manager and click the lock button to unlock to make changes. Then under "Directory Browser" click on "config" in the second column, then click on "AppleFileServer". Below you will find a "Property" and "Value(s)" columns. Go to the "idle_disconnect_flag" property and you will see that it has a value like this:
GuestUsrDisconnect_ON ,RegtdUsrDisconnect_ON ,AdminUsrDisconnect_ON ,OpenFileDisconnect_ON
Notice how each flag has an "ON" at the end of it. You can change this to either "ON" or "OFF". I made mine so that if you are an admin on the machine your trying to mount, that it would keep the volume mounted ALWAYS by changing this value: "AdminUsrDisconnect_ON" to this "AdminUsrDisconnect_OFF". My iMac now has kept my G4's hard disk mounted for over 5 hours without disconnecting and life is wonderful.
IMPORTANT! First, for this work properly you must make this change on the Mac that you are trying to mount, not the client. Second, you must save your changes in NetInfo Manager and Restart/Log Off your computer.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020221095151538