Hi Brian,
Please check your MIME settings. The path is System Administration > System Configuration > Knowledge management > Content Management > Utilities > Mime Type. Note 1062725 provides hints for office 2007. You should also check you URLGenerator Settings System Administration > System Configuration > Knowledge management > Content Management > Global Services > Show Advanced Options > URL Generator Service. The viewer field and content access path field should have a value of /irj/go/km/docs.
Best regards,
Duncan