Animation with Tk

[Nick Perkins]

How can I run a timing loop in a Tk app?
I would like to use the Tk.Canvas widget to try some simple animation.
It has some cool features.
I need to have an animation loop, but also have working buttons, etc,
which means running the tk mainloop.

I have tried to use the sched module, sheduling a function that
updates the canvas and then reschedules itself.
However, the run() method does not return immediately, which would be
nice, it just goes to sleep.
Consequently, I can not seem to get Tk.mainloop() to run
at the same time as a scheduler.
Since I am using Windows, I don't think I can fork().

How can I run a Tk mainloop() and also an event sheduler, or
some other type of timing loop?