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.
An XML namespace is just a method in which you can define that your that types belonging to some URI which is a kind of address. It's main goal is to avoid name collisions when you and someone else are defining the same names for the elements. By defining a namespace for which you're only responsible you will be sure that you don't use the same name.
The target namespace is the namespace where newly created elements and attributes will reside when you create them within an XML-schema.