Thankfully, Microsoft added no new data analysis features to Excel 2003, so the book is still quite relevant. The exception would be if you have a lot of XML data that you want to import. Excel 2003 supports XML transformations, but the book does not address them.
The book is perfect for Excel versions 2000, 2002 (XP), and 2003. If you have Excel 97 or Excel 95, the concepts will still work, but the pivot table wizard screen shots will be slightly different on your screen than what is shown in the book. The book explains that those versions of the Pivot Table Wizard had four steps instead of 3 steps. The book does show what the missing step looks like, so even if you have those versions, you can still follow along.
Bill Jelen