That was epic
That was amazing, especially for your first flash, although im guessing you've had experience in anmation using other programmes. the one thing i will say, is that you may want to fix the shape tween on one of the blood spurts, it was quite near the end, one piece of the blood crosses over annother piece and they go transparent briefly.
the problem where the audio won't sync, that you was saying about, is because when flash goes on the web, the odd frame is skiped, or one frame lasts a bit longer than it's supposed to (the faster your computer/connection the less it happens), but the music plays steadily so it looses sync. If you goto the frame where the music is placed, and change it from "event" sound to "stream" sound, it forces the animation to stay in sync with the music. Only problem is that streamed audio won't bridge over scenes, and im guessing you've used several cenes, so the only ways round it is to make a new swf for example music.swf with the music in it, then back in the Isamu's Revenge.swf put this code in the first frame
loadMovie("music.swf",1);
the only problem with this, is that you can't upload both files to newgrounds, so the code won't link to anything.
only other thing you can do is cut the music at the time where each scene starts, and put the new fragment in the next scene and so on (if you get what i mean)