Do this little trick to impress and amaze your friends =)

For Microsoft Windows XP -

Go to:
- Start.
- Control Panel.
- Regional and Language Options.
- Click the Customize button.
- Select Time tag.
- Highlight AM and type the name you want to display. Repeat with PM.

click apply and than OK


P.S. - It's a very old trick but still can be helpful for someone I guess.. =)