Sure, you can choose to save files from Word 2008 for Mac as.

We had more issues opening XML files from Word 2008 for Mac in Word 2004 for Mac than we did opening the same files in Word 2007 for Windows. This forces Mac users who often transfer files with Windows users to upgrade. Word 2004 for Mac can’t handle these files without a translator, which at the time of writing Microsoft had yet to release. Word 2008 for Mac supports the XML files that Word 2007 for Windows creates, and vice versa. The only reason we can see for upgrading is to get better interoperability with Office 2007 for Windows. However, with the exception of Elements Gallery and a few minor points, the feature-set is almost intact. Word 2008 for Mac looks cosmetically different to Word 2004 for Mac.