Word Count/Count down

[misstrious]

Hi,

I am looking for a simple way (if possible) of doing a countdown in
word similar to the countdown on twitter.

To explain:

If I want to set a question and expect the answer to be at least 100
words (or 250 characters if easier) I would like to have a countdown
to show the student how many more words they need to write.

I am sure this can be done with a Macro but not sure how so any help
appreciated.

Thanks