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You can find the above page and a lot more in The Animators Survival Kit.  These shapes and such might take a little bit of time to learn, but you’re lucky you have an easy to use reference below your nose!  There’s many different ways of approaching lip sync in Flash, such as using pre-made shapes (symbols) or drawing out everything frame by frame.  I personally like to do it entirely frame by frame, because it lets me play with the emotion in real time and have everything flow a lot better.  If you have limited time, using a library of pre-made mouth symbols is perfect.  You basically just swap the symbols as you go along.

Obviously you need to be able to hear the sound as you scrub across the audio in Flash, which won’t happen unless your audio is set to “stream”.  To check this, just select your frame/layer with the audio and go down to the properties bar (CTRL+F3 if it’s not there).  This will bring up a few options for changing the audio, as the properties bar is context sensitive to what you have selected.

Setting the audio to stream will allow you to hear the audio as to what sound it makes in each frame.  If you have it set to “event” or “start”, you will not be able to do this (these are generally the defaults in Flash).