This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
First of all, do you know what namespaces are used for in XML and how they are commonly used? Probably not, most people don't really understand them. So I would suggest you read a tutorial about namespaces. I am not impressed by the w3schools tutorial, they are quite superficial. The namespace tutorial at zvon.org is more thorough.
When you have done that, I found this paper on how to use namespaces in schemas that looks like it goes through how to configure things quite well.