You might not be able to capture your voice because you have the wrong audio input selected. Try this:
Right click on the video area and click Settings. Then, find the Microphone tab. It will look like this: http://www.macromedia.com/support/documentation/en/flashplayer/help/help03.html
Once you have clicked on that tab, try each of the settings in the drop down box. When you choose a setting, speak into your computer. You will know that you have found the setting that works for your microphone when the indicator bar on the left shows movement.
When you speak at a normal volume, the indicator bar should rise about half way up, and turn yellow. If it does not (it is too high and red or too low and green), adjust the "Record Volume" slider right next to it until it does.
Let us know if that fixes the problem. Thanks for your patience and help!
If you have any questions, feel free to email us or post a question in this topic thread.