Unable to install Microsoft Office 2001 on Mac OS X
Office 2001 isn't designed to run natively on OS X. It needs either OS 9 or some form of translation software.

Apple used to provide this in the form of Rosetta, which was part of the OS X operating system until OS X 10.6 in 2009.
It used to be available as an additional download by launching the App Store, or by installing it from the 'Extras' folder on the original 10.6 installer disks.

I'm not certain if Office 2001 is even actually too old to run under Rosetta, or whether it must be run specifically under the Classic Environment, i.e. OS9.
Office X was released to specifically address that.

The simplest workarounds might be


Get a newer version of Office, that supports OS X [possibly costly]
Get OpenOffice, which ought to be able to work with most Office documents, regardless of age [free]