Help with Countdown please

Hi,
I'm using the Countdown hack by KevinG and also the Dynamic Templates Hack by Logician.

I'd like to be able to allow my members to enter a Date via a form, this date to be stored in the vB database or in a cookie. I'd then like to use this date to produce a countdown - probably using the two hacks mentioned above

What would be the best way of doing this ?

I thought that I could add a field to the User Table to store the date entered by a user. Just dont know how to retrieve the date and produce a countdown from it.

any ideas?