If you use the "Speak text" feature in the Actions preference pane of iChat, it may later stick after you try to turn it off.
Symptom
iChat continues to speak text even though you tried to turn off that feature.
Solution
These steps are a workaround for turning off "Speak text":
You may now reselect "Enable these actions," so that other actions may be used for the affected event. Any time that you select "Speak text" for the affected event, you may have to repeat these steps to turn it off.