Disable the Office Plugin that comes with Symantec/Norton AntiVirus. See http://support.microsoft.com/?kbid=329820 "How to use Office programs
with the Norton AntiVirus Office plug-in" for more information.
See “OFF: Cannot Open Office Documents or Cannot Edit Inserted Objects After
You Install Office XP Service Pack 2 or Office 2000 Service Pack 3†http://support.microsoft.com/?kbid=328613