MS Office 2003 and MS Office 2007 have really a huge Gap (Yes 4 years!!).
The tradition extension .doc which is used right from the beginning of MS Office 97 has been replaced by a new(OK little Old) extension .docx (Document Extended!!).
The problem is that .doc and .docx are different file types and only MS Office 2007 can open both the file types but it is unrecognizable format for the former.
People who use a System with Ok type Configuration Cannot afford run Office 2K7 as it is built with heavy GUI implementation with Memory Eating Components. So they restricted themselves to Office 2003.
The Change from .doc to .docx affected international standard of data storage.
Office 2K7 users have no Problem as they can save it in .doc format.
But Office 2K3 users was not able to open .docx till they read this Article. As they came to know that there is a Compatibility pack and they can just download it by CLICKING HERE