My buddy Shankar pointed me to this on XML indexing. It's an interesting topic since figuring out smart ways to index and search XML is a tough job.
Here's the paper: http://www.vldb.org/conf/2004/IND5P2.PDF
It talks about compression, tokenization, path indexing, etc, etc. If you're serious about XML and SQL Server 2005, you should read this paper.
Enjoy!
Tom