One of the interesting things advanced by Microsoft over the years has been features designed to ensure documents or files created in one version of Office are compatible with documents or files created in another. The key to this has been something that's been floating around in the software world for years: backward compatibility. What that means, in a nutshell, is that new versions of software should be able to read most (perhaps all) documents or files created in previous versions. This hasn't always been the case; nor has 'forward compatibility' always been available.
One of your greatest tools you can use to overcome this--whether with Microsoft or other software--is simply this: the use of Save As.
When you save a document or file "As", you're instructing the software to save that thing as something other than its native format, or to save it somewhere else, or to save it with some other name. So for example, when I have a Word 2007 (or 2010) document I want to Save As, my goal is usually to ensure it can be opened and/or read and/or edited by someone using an earlier version of Word.
Word has for some time had a built-in and largely automatic feature called the Compatibility Checker. Under some uses of Save As, or when you instruct Word to ensure the document is compatible with earlier versions, the Compatibility Checker pops up. Usually, it simply tells you that some minor formatting will be affected. So here's my tip: keep the document open in such cases (instead of saving it on closing). Re-examine it. You may discover that one of those minor formatting issues has adjusted, for example, the way the text in a footer is aligned. Once you've saved with Compatibility, go over the document again and make the little adjustments as necessary. Re-save. That should do it.
Office 2010 is on the way. In fact, there have been at least two beta (testers) editions. I was invited in on the first, but the second is open to everyone. The interface is slicker, and less troublesome, and it has been trimmed down. Some nice new bells & whistles too. If you're a fan of the new Office look and feel, I think you'll like Office 2010.

