In a previous post I mentioned I wanted an IRC notifier; I got the notifier working but can't really plug it into xchat.
As far as I can tell (and I didn't look that much, the only way I can get the notifier to fire when xchat matches my username in a message is to use the sound infrastructure. Each event can have sound play, and you can specifiy the program to play the sound. Thus I use this with a bogus filename like " You've got a message" ... the only problem is the box has the full path to the filename in it.
xchat must have a better way to handle this sort of thing ...