If you Google that question you find a number of sites explaining that docx files (Office 2007 files) cannot be opened by Office Word 2003 or earlier and that you will need to download install all 27 megs of a compatibility pack made available by Microsoft. There are also several online document converters that supposedly convert docx files to PDF or doc files but in my experience they either don’t deliver or they charge.
The simplest way to open a docx file is to email it to your Gmail.com account, and then to view the file as html, which lets Gmail do all the converting, and save you a lot of hassle!