Microsoft has released the Office Open XML File Format Converter for Microsoft Office 2004 for the Mac. This updater enables Mac Office 2004 to open and save files in the OOXML format supported by Microsoft Office 2007 for Windows and Microsoft Office 2008 for Mac.
Personally I uninstalled Microsoft Office 2004 from my Mac about a month ago due to massive instability and hangs, and haven't missed it. I tried updating to the latest point release first, but they're about a dozen different updaters that have to be downloaded and applied in a specific order and who has time for that? Instead, I've been using Google Docs for the limited amount of Word docs I need to read. I suppose if I were writing another book, I might have to reinstall Word, but short of that I just don't the see the need.