I rarely go log into IRC channels, and had not done it after I got this laptop last summer. When I do (there will be an unbutuforums meeting I can attend in a few minutes), I use xchat. I know there is a whole set of IRC clients, but this is the first one I used, and it fits my very basic needs.
Surprisingly, there was no sound on this default fresh install (Ubuntu Hardy). I created a ~/.xchat2/sounds file which was missing and copied a .wav file from /usr/share/sounds, then enabled it from xchat preferences menu. All set!
Looking around, I found a xchat-gnome package that I will try soon.
b-initials 
Same problem for me. xchat has no sounds folder
The sound folder exists in Karmic xchat 2.8.6, but is empty..
XChat by default doesn’t come with the sounds folder anymore. If you need sounds you can create it under home/.xchat2/sounds/ and then place whatever files you want in there. I thought it was kind of silly that they don’t include any sounds on their own!