Can anyone comment on the possibility of success were I to use these two versions of Word to edit the same files, back and forth between the two versions, over a period of time, and with a good deal of changing between the one and the other?

There are ways of making them work together, I realize (e.g., the "Word 98 Converter" for Word 5.1), but with what trouble? Has anyone tried this and and failed, or is the process as seamless as the Word 98-2004 transition proved to be?