Materials: You need a microphone and a way to upload your voice.

Plug in your microphone.
On your task bar, and go to Start >> All Program >> Entertainment >> Sound Recorder.
Press the recording button (red circle) on the sound recorder and speak into your microphone.

Save it.
Upload your voice and get the URL.
Put a link on your page to the uploaded sound.

-OR-

You could use the code that people can only here your voice once when they enter your site.