How can I get desktop notifications on irssi?
There seems to be a couple kicking about:
https://github.com/stickster/irssi-libnotify (previously at http://code.google.com/p/irssi-libnotify/)
or..
http://wahjava.wordpress.com/2008/06/15/irssi-notifications/
They're just Perl scripts you drop into ~/.irssi/scripts so you could tweak them to suit you.
http://code.google.com/p/irssi-libnotify/ works great for me.
If you want it to notify all messages instead of just hilighted ones remove || !($dest->{level} & MSGLEVEL_HILIGHT) from the script.