Reading .docx documents in Word 2003 is easy. Here's how.
To open .docx files in older versions of Word you need to download the Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint from this link: http://www.microsoft.com/download/en/details.aspx?id=3. You will get a file called FileFormatConverters.exe - just run it and it will install the necessary updates. This will work with Word 2003, 2002 and 2000.
Just in case .docx files aren't associated with Word, right-click on the .docx file you wish to read, select Open With and choose Microsoft Office Word from the program list. If Word is not in the displayed list of programs, select Open With -> Choose Program... and locate Word there.
www.microsoft.com - Open a Word 2007 document in an earlier version of Word