for MyCat....
You're not alone in having problems with needing to make documents usable for people with older versions of Office.
One client had problems as one of several documents he was sent for a tender was in MS Word 2007, saved as XML (file type .docx ) and he was stuck as he couldn't read it.
However, one thing Microsoft does, for Windows machines at least, is provide free document display/print utilities.
In the case of older versions of Office, there's an add-on so it can convert the 2007 Office documents. Then they can be saved by the user (eg with Office 2003) and the saved document can easily be opened and worked on. On a machine with Office 2007 you should be able to open older file formats (and from other spreadsheets, word processors, etc) if you check the 'file type' (I am hoping that it still offers that box, below the one where you enter the filename).
Something that might come in handy, if you have a friend or relative but they are miles away, is www.LogMeIn.com which would allow the other person to 'login' on your PC via the 'net and they can then demonstrate or fix problems.
I've used it for the last 2-3 years (clients from Kent to Yorkshire, and I'm in N Wales) but obviously you only want to let someone you really trust get onto your PC.
It's free for the basic version (they have other versions costing annual fees which include file transfers and other things).
I used LogMeIn to update my client's machine so he could use the Microsoft conversion software as he had to get his documents in the post the next day, and he lives miles away (and I don't drive).
There are other similar 'remote control' options but this one is pretty easy to use.
(sorry, went off at a tangent).