I saw that someone searched against this and hit my blog, so I decided to quickly add a note on this.  Office 2003 does run on Windows Server 2008, but there is a problem with the Rights Management System client.  The Knowledge Base support article Release notes for the preliminary release of Windows Server 2008 has the following to say:

Office 2003 is unable to detect the Windows Server 2008 Rights Management System (RMS) Client when you try to use the Windows Server 2008 RMS to protect Microsoft Office 2003 documents.

This is planned to be fixed in the future, but since many people don't use the RMS functionality, this is good news.

Thanks

David