Kuren's TClock recomendation

TClock is THE best freeware program for setting your computers time to be syncronized with an atomic clock.
TClock's home page is this:
http://homepage1.nifty.com/kazubon/tclock/indexe.html

This program is tiny, free, and it even comes with the source code.

You will need to unzip it to a folder and make a shortcut. Put the shortcut in your startup folder so it always runs when you boot windows.

Next you will need to tell TClock which atomic clock to syncronize with.
find one near you from the links at the bottom of this page:
http://www.eecis.udel.edu/~mills/ntp/clock1.html