This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
You can't use Word for editing, but you may be able to mimic its interface in the web application. The saving (on the server) will then trigger a save (on the server side). This won't be easy though; Office doesn't cost a lot of money for nothing. Can't you use Google Docs or a similar service that has already tackled this problem?