I have MS Office 2003 at work and I downloaded and installed the MS
File Compatibility Update that is supposed to allow reading the 2007 files.
I have yet to make it work.
There's a shareware program called DocXConverter that does a
pretty good job and costs $19.95, otherwise it only does part of the file so you can see it works.
There is a donation-based site (www.zamzar.com) that will convert files
for you and email them to you. They had trouble converting the
one XLSX file I uploaded. That wasn't a complete shock though
because by that time I had read online about how some folks
WITH Excel 2007 had trouble reading XLSX files sent to them
that were created on a different computer!
I haven't given up on Zamzar yet... if I get a
different file I'll try it again.
It appears MS has given us a box of bugs to open.
Surprise, surprise.