Sorry, I've been working on a tricky network issue for a couple of days.
what happens when you run the command from the command-line on the alert server?
C:\Program Files (x86)\Growl for Windows\growlnotify.com /a:"Orion" /t:"A Network Node is Down!" /host:10.154.100.1 /pass:"mypass" "Test"
if that does not display "test", and you get an application not registered error try:
C:\Program Files (x86)\Growl for Windows\growlnotify.com /a:"Orion" /t:"A Network Node is Down!" /host:10.154.100.1 /pass:"mypass" /r:"General Notification" "Test"
and then try
C:\Program Files (x86)\Growl for Windows\growlnotify.com /a:"Orion" /t:"A Network Node is Down!" /host:10.154.100.1 /pass:"mypass" "Test"