Simply chuck it in your ~/.irssi/scripts and symlink to autorun.
Very simple change, but it was nice to have dunst show irssi PMs etc for people who subscribe to the dmenu mentality.
I recently switched from Pidgin to IRSSI/Bitlbee for all my chatting needs, and was a bit sad that the normal notify.pl didn't seem to work with dunst... I'm not sure what you changed, but it worked, so thanks a lot!
"Some humans would do anything to see if it was possible to do it. If you put a large switch in some cave somewhere, with a sign on it saying "End-of-the-World Switch. PLEASE DO NOT TOUCH", the paint wouldn't even have time to dry."