I have Office installed on my Mac, so it reads .doc and .docx files. If the whatever other editor it has can read .doc files, I'd agree that's the best choice. I'll check it out.
Edit: Yes, TextEdit on Mac OS X Snow Leopard can read and edit .doc files. They open with a border around them in a larger window, but they can be edited and saved in .doc (Word 97, Word 2003 and Word 2007) format. When they're opened with Office on the Mac, you don't see the border around the document -- it fills the whole window.
The Linux people can use the OpenOffice word processor, which Ubuntu has installed by default (version 3.2 of OpenOffice is what I have) and it saves Word 6.0, Word 97 and Word 95 files.
It looks like Word 97 is the best bet.