You didn't mention which version(s) of Word and Excel were used to create the documents, or which version(s) you're using/trying to use on your Mac.
If it's (Windows) Office 2003 or earlier, Microsoft released a metadata management tool that might help you understand, and perhaps edit some of the metadata there now. The tool is available for (free in the US, at least) download here -->
http://office.microsoft.com/en-us/help/HA011400341033.aspx
It is possible that 'read-only' status was set in some version of the file (perhaps copied to a CD at some point?), and remains set to 'read-only'. One fix is to open it (in Windows) and clear the read-only status. Windows discussion here -->
http://ask-leo.com/whycant_i_open_thisfile.html
Another possibility is to try opening the documents with a different program (OpenOffice, iWorks Pages, iWorks Numbers) that can open and read many versions of Word and Excel files.
In my experience with earlier versions of OpenOffice, I've had problems with formatting changing (e.g. text document fonts and formats) when I've opened documents with OpenOffice and then attempted to re-save them in Word (doc or docx) format. I don't recall using OpenOffice with Excel files. I'm not currently using OpenOffice, so I can't say whether the problem was fixed or not.