NirCmd utility has a 'speak' command that allows you to easily cause your computer to speak the text that you wish. In this command, NirCmd uses the Speech library (SAPI) that is installed with any instance of Windows XP and Windows Vista. The speak command is not the most useful command in NirCmd, but it's a nice and funny addition for your daily computer use.

Here's a few examples of what you can do with the new speak command:
nircmd.exe speak text "Please don't touch my computer !"

If you want to wait 60 seconds and then speak something, you can try this: (60 seconds = 60000 milliseconds)
nircmd.exe cmdwait 60000 speak text "Get out of my room !"

If you want to speak the text that is currently in the clipboard, use this:
nircmd.exe speak text ~$clipboard$

If you want that the computer will speak the entire content of a text file, use this:
nircmd.exe speak file "c:\temp\speak1.txt"

Be aware that Windows XP comes with a default "robotic" voice known as "Microsoft Sam", while Windows Vista provides much better woman voice, known as "Microsoft Anna".