Office 2007 and Office 2008 use a new XML-based file format (.docx,
..xlsx, etc). All apps in both suites have the ability to use the old
97-2004 format instead (use Save As), which Office 2000 will be able to
read (.doc, .xls, etc)
Otherwise, you'll need to ask some Windows-using people whether there is
an update or download that gives Office 2000 the ability to read the new
file format. Start here:
http://www.microsoft.com/office/community/en-us/FlyoutOverview.mspx
Entourage, which does not create files that are exchanged with Office
2000 users, seems irrelevant here. If you have a question, try asking it
in plain language, with supporting details.