This is what I use as a countdown script.
Download this flash file:
http://www.mediafire.com/?gnzkdlzzmuh
Upload to your server.
Then put this html code in a text widget:
<object type="application/x-shockwave-flash" data="http://www.your-url.com/countdown.swf?mo=12&da=31&ho=10&co=000000" width="250" height="100">
<param name="movie" value="http://www.your-url.com/countdown.swf?mo=12&da=31&ho=10&co=000000" />
<param name="wmode" value="transparent">
</object>
Change out mo= with the number of the month; da= with the number of the day; ho= with the hour; and co= with the 6 digit color code you want the countdown text to be.
You must put the data in the <object> and <param>.
Good luck!