Word 97-2003 works jusy fine!
I used Microsoft Word 2010 for both of my novels and everything worked fine. The only thing I noticed was that bullets do not show up properly once the document is converted into the ePub format. If you can, I would recommend saving your book as a Word document and going from there.
Secrets: A Willow Ryan Novel
Promises: Willow Ryan Book Two
I used word (.doc) It uploaded with no problem and then you can view it in their nook simulation viewer to make sure everything looks the way yoy want it to. I had to play around with mine several times in order for it to appear the way I wanted. I eneded up having to delete my page numbers and using page breaks in order for the chapters to end correctly.
Don't give up!