Welcome, hope you enjoy your stay!
I presume this will be included in detail in the
2.3 Manual
Otherwise, this page should have some relevant information:
http://intrr.org/blender/audiosequencer.html
One thing to remember, is that Blender currently does not yet support saving the audio within an AVI or QuickTime file. You'll have to use the 'Mixdown' button to export a WAV of your final mix, which you can then combine with the video in an external video editing application.
Questions regarding how to use blender are also currently best asked at the main blender user community site:
http://www.elysiun.com . The community there is huge and very helpful. This forum is mainly meant for discussing the development of Blender itself.
Cheers