i think every flash coder ends up writing some kind of verlet integration demo. here's mine:
i plan to use this for the monkey pet as he swings around.
what, no source code? sorry, the code is such a mess that it's embarrassing!
(i am also aware of flade, the flash dynamics engine, but (a) i thought i'd learn more doing this myself, (b) flade is actionscript 2.0 and my pets are still written in actionscript 1 (although i may upgrade the pet code someday) and (c) i don't need all of flade's features — the only physics i really need is gravity. i haven't looked at any of the code in flade…)