Open the rtfd file in TextEdit, choose "Save As..." from the File menu, and select one of the Microsoft Office formats from the menu at the bottom the save dialog. TextEdit can save to .doc or .docx.
If for some reason this doesn't work properly, you might want to try the same thing with OpenOffice instead of TextEdit. OpenOffice has better compatibility with Microsoft Word files than TextEdit, so it might produce better results. For simpler documents, at least, TextEdit should do fine, though.