The catagorised icon mod by Chiz let's you do this. I have it on mine and lets you set the values for the smilies in admin. ie, :) produces what your looking for.
I believe you can achieve what you want by editing inc_functions.asp to accept the value ;) instead of the current code for
Try removing the ['s and ]'s from the smiley codes in inc_functions.asp, but remember to keep a backup copy of your current file before you make any changes!