If you just want to animate, here's some opensource animation tools:
, a lightweight animation program. Kinda goes with a flipbook-ish work flow.
is a bit more heavy duty, they feature some great movies in their gallery. But the program itself is very
complex, so you might encounter a cliff-like learning curve.
If you want the flash aspect, SWFTools
might help you out.
That's all I can think up at the moment.