When using growlnotify be sure that the user on the computer displaying the growl messages has privileges to run terminal. Open Directory allows admins to prevent access to applications. I have terminal access blocked for most of my users. This block was preventing access to growl notify.
Here is an example of what to use with the applescript step in FileMaker to send growl notifications.
do shell script “usr/local/bin/growlnotify -m ‘message here’ -H 192.168.1.1”
The receiving computer has to have listen for incoming connections enabled under the “network” tab of the growl preference panel.