I found this in a few different places around the 'net - hopefully it's helpful:
Add a Voice Message to an E-Mail Message
Personalize e-mail with a voice message? You can perform this task using the Windows XP Sound Recorder and a microphone. First, open the sound recorder:
Click Start, click Programs, click Accessories, click Entertainment, and then click Sound Recorder.
On the File menu, click New.
To begin recording, click Record, and to stop recording, click Stop.
Save the .wav file to a folder of your choice.
Attach the file to an e-mail message.
To record sounds, your computer must be equipped with a microphone. Recorded sounds are saved as waveform (.wav) files.
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