Here's an Applescript example which uses the standard os x notification :
Code:
set hostName to "192.168.1.15"
try
do shell script "ping -qo -c 3" & space & quoted form of hostName
on error
display notification "Host" & space & hostName & space & "is down."
end try
If you want to use Growl then take a look at the AppleScript Sample from the link. You can also use GrowlNotify from the command line.