Tip: Make iChat speak your messages in Leopard
Leopard’s new Alex voice is much better than the voices included in previous versions of Mac OS X. In fact, Alex is good enough to use in iChat, where you can have messages read to you as they arrive. It’s a surprisingly nice effect.
Here’s how to tell Alex to read your messages in iChat:
1. Open iChat Preferences.
2. Click the Alerts tab.
3. Choose Message Received from the Event popup menu at the top of the window.
3. Turn off Play sound.
4. Turn on Announce when event occurs.
Your window should like this:

When you’re working with iChat hidden in the background and a message comes in, it can be handy at times to hear Alex speak up.
Unfortunate that this is so poorly “explained” in the Alerts dialog. Those options make it look like it will just announce that a message has arrived, the way it used to work in Tiger.
And that’s what it just does - only speak some events, but NOT the message.
Forget my comment - the first time I haven’t deactivated the “Play sound”…