Here’s a feature that Office 2003 has (and maybe Office XP, too) that Office X for the Mac doesn’t. Somewhat to my chagrin. In Office 2003, you can import an arbitrary XML file, with or without a DTD, into a regular old Excel worksheet.
Why might you want to do such a thing? Think data acquisition and analysis on the cheap, without having to write an XML parser to understand the data. Say, for instance, you’re bringing in about 200K of XML data from Weblogs.com every hour for two weeks and you want to look at, munge, and export it quickly to a format that can be imported by a SQL database. Possible using Excel 2003. Not possible using Excel X for Mac.
Little known not-secret: Excel X for Mac is a completely separate code base from the Windows versions of Excel, produced by a different team in a different division. Good news: this means it acts more like a Mac product (remember Word 6?). Bad news: sometimes major features go missing.