I've only used FLVs in Flash 7. If you are using the
NetStream technique you will need to attachSound to attach the
audio portion of your FLV to a clip. You can then use the regular
sound object methods.
PS: I'm not sure if daniel@senap's technique will work or
not, but I think it won't allow you to control the FLV sound
separate from other sounds in your file. I do know that my approach
is a bit more complex, but it allows independent control.