You can't disable the back button and this will not solve the original poster's issue.
Look in our JSP FAQ for articles on no-cache headers and the Post-Redirect-Get pattern. The combination of these two things will greatly reduce the likely hood that someone will back into a page with stale data on it.
The user's browser is theirs and the developer of a particular app or page has no business tinkering with the way it works. Think of your app as a guest in the user's house. Make sure it can handle back button and refresh button clicks gracefully instead of trying to defeat them.