So, this seems to be a problem limited to Word and Excel. Opening files from the same Mac folder with other applications (e.g., PowerPoint) on the Windows machine works just fine. This is followed by a dialog asking 'Do you want to retry the save?'.
Opening, changing and then saving a Word doc results in the following msg: 'Word cannot complete the sae due to a file permission error. When I then re-open the file, I get the original messages again and then another 'Cannot access '.
Please close the document and try to open it again.' When I respond to this msg, I get another one 'The document was saved successfully, but Excel cannot re-open it because of a sharing violation. The document may be read-only or encrypted'. When I change excel files sitting on my iMac (OSX 10.5.6) from my Windows XP SP2 machine across my LAN, I'm presented with a dialog with the message 'Excel cannot access.