Here. "Microsoft XML Diff and Patch is a set of tools for comparison of two XML documents and application of the changes (patching). XML Diff detect addition, deletion and other changes between two XML documents. It also detects structural changes like a move of a XML subtree. It produces Xml Diff Language Diffgram (XDL diffgram or just diffgram) that describes the differences between the two XML documents. The diffgram can be then used to display these differences or to perform a patch operation using the XML Patch tool."
I know that this tool has been sorely needed in the XML community for a while and now MS has released one.