I remember back to the old days of my Commodore 64 . Way back in the early eighties, I had a command line program to be able to have the computer say what you type on the command line. I was very surprised that nothing like this is freely available on the net for windows. Microsoft provides both the "MS Agent" COM api as well as the SAPI api, but no easy way to utilize either.
This is a real simple program that simple uses the MS SAPI api. Simple run "Say.exe Hello world!" and have your computer say hello to the world.
Here is a link to a statically linked EXE: SayStatic.exe
Here is a link to a dyncamically linked EXE (MSVCRT.dll version 8 / Visual Studio 2008 (9) ): SayDynamic.exe
Here is a link to the source code.
Put it up on a publically accessible network share and use System Internal's psexec.exe (now owned by Microsoft) and have fun freaking folks out.