Windows XP by default allows you to have one only clock, but in Windows 7 you can have three clocks belonging to different time zone. Here are the steps how to enable them on your machine,
1. Go to Control Panel, Click Clock, Language and Region
2. Now click Set the time and date under the heading Date and Time, you will get this screen
3. Now click Additional Clocks tab, so that you can see the screen as shown below
4. You can now see there are two checkboxes Show this clock
5. Click the first checkbox – Show this clock, and select anytime that you want. for example – US & Canada
6. Click the second checkbox – Show this clock, and select anytime that you want. for example – London
7. You can also name these clocks, by entering them in Enter display name. For example for clock1 it is US and clock2 it is UK, as shown above.
8. Now say OK
9. Mouse over the clock in your system tray to see three clock timings, by defualt your local time, US time and UK time.
10. Click the clock icon from your system tray to display all the three clocks.