Calculator is part of your Windows system not Office. If you have Windows
XP, you can re-install from Control Panel, Add/Remove Programs, Windows XP
components. If the box for the calculator is checked, clear the check,
reboot and go back and check the box.
You would need to get off of your Operating System CD, it isn't part of
Microsoft Office. How? Ask in a group that answers questions about the
Operating system your are using. A list is at the link below.