If the formatting of the Word file is fairly standard, amazon has a service where they'll convert .doc and .docx files into .azw for you, although it sometimes doesn't handle odd fonts or characters very well. You can send the file as an email attachment to [username]@free.kindle.com and a few minutes later it'll be emailed back to you in the kindle format. (If you send it to [username]@kindle.com instead, it will convert the file and send it directly to your kindle, although there is a small fee for that -- ten or twenty cents, I think.)