how to re-insttll OLD version of Office (X)

Hello

This is an OLD question -- I have not updated MS Office for a long
time ( a long story ) -- and am moving from really old computer to a
newer on --  I have an UPGRADE from Office to Office X --that looks
for the version 9 software ....but this computer doesn't have any
version 9 software whatsoever .... any idea how I can install the
software --I have a valid serial #.

Regards

Greg H