Yup, it's true. There's a catch though.
To get Microsoft Office 2008 for Macintosh upgrade, you must purchase Microsoft Office 2004 between September 25th 2007 and March 15th 2008. Visit the Microsoft Office 2008 promotions site to get all the details.
As a reminder, there are numerous alternatives to Microsoft Office for Macintosh that I listed in a previous blog posting. There are even more that I didn't list, many of which can already read the new document format used by Microsoft.
Erik