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.
As Paul said - to put spaces in an XML document, you just put spaces in the document. It's a text file. There's nothing magic about it. Which is why I suspect you're really trying to ask something else.
At a guess, you're trying to put spaces in the result of some process acting on the XML file. But without knowing what that process is we can't help you. Can you explain further?