software to synchronize animation and sound?

[igowerf]

My friend and I draw cartoons that we animate and make into AVI movies. It's nothing professional but I was wondering if there is any good software that'll let you make avi's frame by frame. Right now, I'm using Animation Shop to make the animation and then I use a freeware program called Soundtrack Producer to add sound. This is very difficult because I try to time the sound effects or music to the animation. Is there some software that has both of these functions combined so it's easier to synchronize the animation and sound? I see a lot of flash cartoons where the animation is timed nicely to the music/sound. How do they do that? Thanks a lot.