Beatle Atomic Time synchronizes you PC's clock with an Atomic Time server, and shows you the correct Swatch Internet Time.
This program not only allows you to use atomic time but also features a higher resolution time (1/100 beats) and a more precise counter running in its own thread to keep the displayed time within one millisecond resolution.
You can also update your System clock to the proper atomic time, and use the built-in Swatch Internet Time to normal time converter.
Beatle Atomic Time can run as a convenient icon in the System Tray area of the Windows taskbar.