I upgraded from Office 97 to Office 2007 and haven’t had any trouble. It takes a little getting used to and some of the features are in less than intuitive places. But that’s a quick learning curve. I bought my copy of Office 2007 (Home/Student Version) for $149 at Office Max. It allows 3 legal installs using the same product key. So far, so good.
What annoys me is the fact that if your computer fails (Vista Cough!) 3 times you have to buy a new copy.