There are applications to download for a wii count down but i find the best way to have one on your desktop is to make a desktop item.
Step 1 RIGHT click on your desktop
Step 2 click Properties then the Desktop tab
Step 3 click the Customize Desktop button
Step 4 click the Web tab
Step 5 click the New button type in http://www.wiicantwait.com/ and press Ok.
After you click ok close all the windows you opened and look at your desktop you should see something similar to this
You can resize it as you wish and it won't interfer with anything on your computer except maybe your icons which you can eather move or hide.