Windows XP includes a simple text to speech feature. You can do the same thing on the command line with the program Festival, which is in the Ubuntu 6.10 repositories.
apt-get install festival
Once Festival is installed you can start its prompt by typing festival. Use it like this when in Festival’s prompt:
(SayText "Your computer is speaking this text.")
Read a file out loud with this command:
festival --tts reading.txt
The coolest part is yet to come! In Ubuntu 7.04, the repository includes festival-gaim, which will speak out what your friends are typing to you in Gaim. Of course you can alway go all the way and use Skype if you want to eliminate reading and typing.
apt-get install skype